Rozprawy doktorskie na temat „PMMA thin films”

Each year millions of people suffer from bone defects resulting from trauma, tumors or bone-related injuries. Therefore there is a need to continuously develop new materials or improve the properties of the materials currently used, for bone replacement or implant applications. Polymethyl methacrylate (PMMA) has proven to be a promising alternative as a material for implants; however, there are still some limitations inherent to this material, particularly related to its surface properties. This thesis work is focused on the fabrication of hydroxyapatite (HAp) thin films on the surface of 3D printed PMMA substrates. 3D printing, particularly the Fused Deposition Modeling (FDM) technique was used to fabricate PMMA substrates with different surface porosity levels. FDM technique exhibits the potential for fabricating customized freeform structures for several applications including craniofacial reconstruction. HAp thin films were deposited by Radio Frequency Magnetron Sputtering (RFMS) and Ion Beam Sputtering (IBS) techniques, with a commercial target and an “in house” sintered target, respectively. A structural, chemical, mechanical, and morphological characterization was conducted in the generated surfaces by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and hardness and roughness measurements. The results of the XRD analysis revealed an amorphous structure for the films produced by both RFMS and IBS techniques on the PMMA substrates. The micrographs obtained by SEM showed a columnar morphology and a low density for the films produced by RFMS; the same technique revealed a structure of ridges of standing platelets with curved contours for the IBS deposited films. The amorphous structure and the morphology of the films, as well as the hardness and roughness can be propitious to improve surface properties and promote the osseointegration capabilities of PMMA. This work contributes to the basis for the development of a PMMA implant manufacturing process using 3D printing and HAp film deposition techniques, with improved osseointegration properties.
Cada año, millones de personas sufren defectos óseos como resultado de traumas, tumores o lesiones relacionadas con los huesos. Por lo tanto, existe la necesidad de desarrollar continuamente nuevos materiales o mejorar las propiedades de los materiales utilizados actualmente, para aplicaciones de reemplazo óseo o implantes. El polimetilmetacrilato (PMMA) ha demostrado ser una alternativa prometedora como material para implantes; sin embargo, todavía existen algunas limitaciones inherentes a este material, particularmente relacionadas con sus propiedades superficiales. Este trabajo de tesis se centra en la fabricación de películas delgadas de hidroxiapatita (HAp) en la superficie de sustratos de PMMA impresos en 3D. La impresión 3D, particularmente la técnica de modelado de deposición fundida (FDM), se utilizó para fabricar sustratos de PMMA con diferentes niveles de porosidad superficial. La técnica FDM exhibe el potencial para fabricar estructuras personalizadas de para varias aplicaciones, incluida la reconstrucción craneofacial. Las películas delgadas de HAp se depositaron mediante técnicas de deposición catódica con Magnetrón y radio frecuencia (RFMS) y deposición catódica con haz de iones (IBS), con un target comercial y un target sinterizado "in house", respectivamente. Se realizó una caracterización estructural, química, mecánica y morfológica en las superficies generadas por medio de difracción de rayos X (XRD), microscopía electrónica de barrido (SEM), espectroscopía de energía dispersiva (EDS) y medidas de dureza y rugosidad. Los resultados del análisis de XRD revelaron una estructura amorfa para las películas producidas por ambas técnicas RFMS e IBS en los sustratos de PMMA. Las micrografías obtenidas por SEM mostraron una morfología columnar y una baja densidad para las películas producidas por RFMS; la misma técnica reveló una estructura de crestas de plaquetas con contornos curvados para las películas depositadas IBS. La estructura amorfa y la morfología de las películas, así como la dureza y la rugosidad pueden ser propicias para mejorar las propiedades de la superficie y promover las capacidades de oseointegración del PMMA. Este trabajo contribuye a la base para el desarrollo de un proceso de fabricación de implantes de PMMA usando impresión 3D y técnicas de deposición de película HAp, con propiedades mejoradas de oseointegración.
Tesis

Morphological development during crystallization of thin films of poly(ethylene oxide) (PEO) / poly(methyl methacrylate) (PMMA) blends has been reported. Studies have focused on the effects of the blend composition, PMMA molecular weight, film thickness, and crystallization temperature on the observed crystal morphology. As the blend composition was varied from 90 to 30 wt% PEO, the crystal morphology varied from spherulites to needles and dendrites. Variation of the crystallization temperature and PMMA molecular weight resulted in similar changes in morphology. A morphological map demonstrating the roles of the experimental controls on the observed crystal morphology has been developed. This map was used as a tool for more detailed studies of the observed morphologies and morphological transitions. The dendritic region of the map (~ 30 = 40 wt% PEO) was studied in detail. Changes in the diffusion length were achieved through variation of the PMMA molecular weight, and were shown to influence the secondary sidebranch spacing. Sidebranch spacing measurements revealed that coarsening of the dendritic microstructure occurred well after the competition between diffusion fields of neighboring dendrite arms vanished, indicating the existence of another coarsening mechanism. These studies of dendritic sidebranching indicate that polymer dendrites develop by mechanisms similar to those in small molecules and metals. A number of in-situ observations of morphological transitions have also been reported, including a dense-branched morphology (DBM)/dendrite transition, a DBM/stacked-needle/needle transition, and a transition from dendrites with 90o sidebranching to dendrites with 45o branching or a dense-branched morphology, both of which grow at 45o to the original dendrite trunk. The DBM/dendrite transition occurred over a range of crystallization temperatures, indicating that the transition is not sharp. Crystal growth rate measurements verified this result. The DBM/stacked-needle/needle transitions demonstrated distinct jumps in the crystal growth rate, indicating a change in the growth mechanism or direction. For the transition involving a change in the growth direction, the effective level of noise (fluctuation) was found to be important in morphological selection. The results of this work have helped to define new directions for the study of crystal morphologies, especially in the areas of spherulite formation and dendritic growth.
Ph. D.

The surface-specific technique of vibrational sum frequency spectroscopy (VSFS) can provide vibrational information about chemical bonds at surfaces and interfaces. Two photons, of visible and infrared frequency, are spatially and temporally overlapped at a surface/interface to produce a photon at the sum frequency (SF) of the two input photons. As well as this process only being allowed in non-centrosymmetric media (i.e. VSFS is surface/interface specific), the SF process is enhanced when the IR beam is resonant with vibrational resonances. Broadband VSFS has been used in this project to study surfaces of two distinct classes of materials, namely graphene and polymers. Firstly, broadband VSFS was used to investigate the heating polymeric thin films using a home-built heated sample cell. The cell was tested using self-assembled monolayers (SAMs) of 1-octadecanethiol (ODT) grown on gold substrates. It was subsequently used to investigate thin films of poly(methyl methacrylate) (PMMA) of four different thicknesses and two different molecular weights that were spin-coated onto gold substrates. It was shown that the monolayers of ODT become disordered upon heating and solidified to incorporate the disorder introduced by the heating process. The PMMA films were also shown to become more disordered as a function of temperature. Secondly, broadband VSFS was used to investigate modified graphene, motivated by the fact that modifications to pristine graphene, be it intentional (i.e. functionalisation) or unintentional (i.e. contamination), cause the properties of graphene to change. This project focused on studying hydrogenated graphene, N-methylbenzamide functionalised graphene and contamination on commercial graphene. A method for calculating the number of hydrogen atoms in a hydrogen island was developed. VSF spectra of CH stretches in N-methylbenzamide functionalised graphene were obtained. Residues on commercially bought graphene were detected using VSFS and RAIRS. These residues were assigned to PMMA that remained on the CVD graphene by the process of transferring the CVD graphene from the copper foil on which it was grown onto the gold substrates.

Block copolymer/inorganic nanoparticle hybrids draw great attention of scientists from various areas for their potential applications in diverse fields such as microelectronics, sensors, and solar cells. Inorganic nanoparticles (NPs) can be expected to be incorporated into block copolymers with order and selectivity by self-assembly of NPs and/or by synergistic self-assembly between NPs and block copolymers. The morphology and nanostructure order of block copolymers can be also adjusted and directed by incorporation of NPs. In this study, the effect of the size and modification of AuNPs on the morphology and nanostructure orientation of block copolymer PPMA-b-PMMA thin films were systematically investigated. The lateral BCP structure in thin films was improved by adding AuNPs. The controlled location of AuNPs in the BCP thin films depended on the particle size and stabilizing species. The re-orientation of cylindrical domains depended on the modification of AuNPs. PPMA-coated AuNPs, corresponding to the lower surface energy component of BCP, were powerful in directing the cylinders from parallel to perpendicular to the substrate. These results provide a general guide for other BCP/inorganic NP hybrid systems for desired morphology and nanostructure orientation.

Di-Block Copolymers (DBCs) are materials composed of two different monomer subunits linked together. These blocks are able to self-assemble in different microphases with various morphologies (cylinders, lamellae, spheres, gyroids). For this reason, the DBCs are widely investigated as patterning and nanofabrication technique. In this work, the combination of conventional lithographic approaches with the Self-Assembly of DBCs is investigated, to develop a new generation of lateral length standards at the nanoscale (under 70 nm) with a low cost approach based on the natural constants of matter. The behavior of a cylinder forming Polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) with Mn = 54 kg·mol-1 within SiO2 periodical trenches by a Rapid Thermal Processing (RTP) oven is studied. Although this material has been widely used as lithographic mask its application in metrology field was still unknown. The optimization and calibration of DBC thin film deposition processes as a function of geometrical and annealing parameters are performed and the characteristic dimensions (L0) of the cylindrical patterns are analyzed. A decoupling of the L0 along the two confinement directions is observed. The center-to-center distance in the direction parallel to the long side of the trenches (L0l) remains invariant as a function of process variability. Thus, the high stability of L0l makes it an intrinsic feature of the system usable as measurand for a new lateral length standard. Finally, the attempt to increase the chemical incompatibility between the two blocks within the PSb-PMMA system by copolymerization of a fluorine containing methacrylic monomer with the methyl methacrylate is performed. The aims are to understand how the fluorine-containing monomer influences the DBC segregation and the structure periodicity, and if this modification allows to obtain a smaller periodicity of the DBC features for potentially increasing the standard length size range.

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

A eletrônica digital desempenha papel essencial no desenvolvimento e manutenção dos padrões de vida em prática hoje no mundo. A peça fundamental para a criação desta era tecnológica é sem dúvidas o transistor. Com o advento de novos materiais, a busca por transistores que oferecem novas oportunidades de processamento e aplicação permitiu que uma nova área fosse criada: a eletrônica orgânica. Transistores de efeito de campo baseados em filmes finos de materiais orgânicos têm recebido grande atenção nas últimas décadas. Apresentamos um estudo experimental e teórico de transistores de efeito de campo a base de filmes finos orgânicos. Foram caracterizados transistores usando um derivado do pentaceno (TMTES-pentaceno) como camada ativa em um dispositivo feito sobre Si/SiO2. Mostramos que a inclusão do semicondutor orgânico em uma matriz polimérica isolante ajuda a manter a estabilidade termo mecânica do dispositivo. Foi desenvolvido um modelo que levasse em conta as resistências parasíticas para explicar o comportamento do transistor em função da temperatura. Também foram construídos e caracterizados transistores usando rr-P3HT como semicondutor e PMMA como isolantes. Apresentamos transistores do tipo Top-Gate e Bottom-Gate com mobilidade máxima de 7 x 10-3 cm2/V.s. Valores de razão ON/OFF de ~ 900 foram encontrados nos transistores otimizados. O comportamento dos transistores é analisado em função da temperatura e os modelos de aproximação de canal gradual e de Vissenberg-Matters foram aplicados para extração dos parâmetros de interesse. Por fim, apresentamos um modelo de corrente de canal baseado na resolução 2D numérica da equação de Poisson usando as idéias de Vissenberg-Matters para a concentração de cargas em função do potencial local. O modelo, embora ainda nos primeiros estágios de desenvolvimento, prevê a saturação da corrente nas curvas de saída simuladas sem limitações de regime de validade.
Digital electronics plays an essential role in the development and maintenance of living standards into practice in the world today. The cornerstone for the creation of this technological age is undoubtedly the transistor. With the advent of new materials, the search for transistors that offer new opportunities in processing and application allowed a new area to be created: the organic electronics. Field effect transistors based on organic thin films have received great attention in recent decades. We report an experimental and theoretical study of field effect transistors based on organic thin films. We characterized transistors manufactured using a derivative of pentacene (TMTES-pentacene) as the active layer in a device and using Si/SiO2 as gate and insulator. We show that the inclusion of the organic semiconductor in an insulating polymeric matrix helps to maintain the termo-mechanical stability of the device. A model was developed that take into account the parasitic resistances and to explain the behavior of the transistor as a function of temperature. We also present the manufacturing and characterization process of transistors using rr-P3HT as semiconductor and PMMA as insulator. We report Top-Gate and Bottom-Gate transistors with maximum mobility of 7 x 10-3 cm2/V.s. The maximun ON/OFF ratio of ~ 900 was found for the optimized transistors. The behavior of the transistors was analyzed as a function of temperature and both gradual channel approximation and Vissenberg-Matters models were applied for extracting the parameters. Finally, we present a channel current model based on the resolution of 2D numerical Poisson equation using the ideas of Vissenberg-Matters to the calculate the concentration of charges due to the local potential. The model, although still in the early stages of development, predicts the saturation current at output simulated curves with no limitation of regime validity.

This thesis presents an investigation into the factors which control the gain and amplification properties in conjugated materials. Conjugated polymers and perylene dyes are highly fluorescent, are easy to process into thin films, and exhibit strong amplification over a broad gain bandwidth making them ideal for use in lasers and amplifiers. The stimulated emission created when thin films of the red emitting polymer poly(2-methoxy-5-(2'-ethylhexyloxy)- p-phenylenvinylene) (MEH-PPV) were photoexcited with high energy laser pulses was investigated. This was characterised by a dramatic narrowing of the emission spectrum which has been assigned to amplified spontaneous emission (ASE). The emission was found to have a gaussian profile and the gain coefficient was found to be 4 cm-1.The temperature dependence of the absorption, photoluminescence and ASE of films of MEH-PPV was measured. The effect of film morphology on the photophysical properties was investigated by using films cast from two spinning solvents, chlorobenzene (CB) and tetrahydrofuran (THE). Film morphology was found to greatly affect the temperature dependence. A particularly important property is the spectral position of the ASE and the factors which affect it. By controlling the film thickness close to the cut-off thickness for waveguiding in the polymer film it was shown that the peak position of the ASE could be tuned by 31 nm. Modelling of the waveguide modes in the polymer films was used to explain this effect. The cut-off wavelength for each film was measured and good agreement with the theory was found. In order to investigate ways in which energy transfer could be used to control the emission, two perylene dyes were used as a donor-acceptor pair in a host matrix of poly methymethacralate (PMMA). The position of the ASE was found to depend on the acceptor concentration. Measurements of the photoluminescence quantum yield and time-resolved luminescence measurements showed that the energy transfer coefficient was 5x10(^11)mol(^-1)d(^3)

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

Magnetic thin films and patterned nanostructures have been studied with respect to their magnetic properties using SQUID-magnetometry, magnetic force microscopy, electrical measurements, and micromagnetic calculations. Properties of vortex domain walls, trapped in Permalloy nanowires with artificial constrictions, were investigated experimentally and by numerical calculations. In particular, the geometrical extent and strength of the pinning potential were evaluated. In these wires, long-range vortex domain wall displacement induced by spin polarized alternating currents was obtained numerically at reduced threshold current densities as compared with the direct current case. Due to the asymmetry of the energy potential, the long-range displacement direction is determined by the vortex chirality. Strained FeCo/Pt superlattices with strong perpendicular anisotropy were investigated experimentally. The strain was controlled by varying the thickness of each alternating layer with monolayer precision and was found to have a dominating effect on the total anisotropy. Epitaxial films of the diluted magnetic semiconductor (Ga,Mn)As were studied with focus on how the ferromagnetic transition temperature could be controlled by post-growth annealing. The ferromagnetic transition temperature was enhanced by approximately 85% for a Mn-doping concentration of 6% under certain conditions. A method to manipulate micrometer sized magnetic particles on patterned arrays of elliptical Permalloy microstructures was studied. Controlled motion and separation of the magnetic particles were obtained using applied rotating magnetic fields. The domain structure of the elliptical elements was studied numerically.

A importância da pesquisa em eletrônica orgânica, se comparada à microeletrônica convencional baseada principalmente em silício, surge pela presença de inúmeros semicondutores e técnicas de deposição de baixo custo e em grande superfície. Os Transistores de Filmes Finos Orgânicos (OTFTs, do inglês Organic Thin-Film Transistors) são a unidade fundamental em circuitos eletrônicos e, geralmente, apresentam a estrutura de um transistor de efeito de campo. Podem ser fabricados sobre substratos plásticos e oferecem grande número de aplicações como: mostradores, etiquetas de identificação por rádio frequência e eletrônica têxtil. Além disso, há demanda por componentes eletrônicos portáteis e baratos, principalmente como sensores em diagnósticos médicos e veterinários in-situ. A geometria de OTFT mais utilizada em sensores na atualidade é a bottom gate sobre substratos de silício altamente dopado e com óxido de porta inorgânico. Polímeros como poli(3-hexiltiofeno) (P3HT) vêm sendo amplamente utilizados pela comunidade científica, atestando o potencial comercial deste semicondutor em sensores. Neste contexto, esta tese apresenta o desenvolvimento de transistores à base de P3HT como sensores na detecção de analitos em fase vapor. O estudo é composto por uma etapa inicial de caracterização da mobilidade dos portadores de carga por técnicas de transiente de corrente, seguida pela otimização do desempenho de parâmetros elétricos do transistor através de alterações no processamento dos filmes dielétrico e semicondutor. Enfim, conclui-se a investigação através do entendimento dos fatores ligados à degradação do OTFT após exposição à atmosfera e sob estresse elétrico, além do detalhamento da sensibilidade e especificidade do sensor. Sensores de P3HT oferecem enorme potencial de detecção de amônia, cetonas e compostos organoclorados. Outros semicondutores poliméricos são provavelmente necessários para maior especificidade em relação a vapor dágua e álcoois.
Research on organic electronics, compared to conventional silicon-based microelectronics, is necessary as it offers plenty of semiconductors and low-cost deposition techniques that can be performed over wide surfaces. Organic Thin-Film Transistors (OTFTs) are the fundamental unity in electronic circuits and, usually, display the metal insulator semiconductor field-effect transistor (MISFET) structure. OTFTs can be processed over cheap plastic substrates and integrate a high number of applications as: flexible displays, radio frequency identification tags, textile electronics and sensors (e.g. chemical and biological compounds). Nowadays, consumers demand portable and low-cost electronic devices, mainly as sensors for in-situ medical and veterinarian diagnosis. The most widely used OTFT structure in sensing is the bottom-gate/bottom-contact FET over highly-doped silicon substrates and inorganic dielectrics. Polymers as poly(3-hexylthiophene) (P3HT) have found increasing acceptance by the scientific community, attesting their potential as semiconductors for commercial applications. In this context, the thesis lies in the development of organic transistors based in P3HT polymer for the detection of vapor-phase compounds. This study begins with transistor performance optimization through changes in dielectric and semiconductor processing. Thin-film thickness and P3HT cast solution drying time are the main studied parameters. It involves also the understanding of device performance degradation when exposed to atmosphere and under bias stress, before finally mapping sensitivity and specificity against gaseous analytes. P3HT-based sensors are potentially interesting for ammonia, ketones and organochlorides detection. Other polymeric semiconductors may be necessary to increase specificity against water steam and alcohol analytes.

Orientadores: Júlio Roberto Bartoli, Elizabeth Grillo Fernandes
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química
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Resumo: Nanotubos de carbono (NTCs) apresentam características interessantes para aplicações em eletrodos transparentes. Quando dispersos em escala nanométrica são transparentes ao espectro da luz visível e são capazes de conduzir eletricidade após atingirem percolação em matrizes poliméricas isolantes. Neste trabalho, é descrito o uso de nanotubos de carbono de camadas múltiplas (NTCMs) na produção de filmes poliméricos flexíveis transparentes e condutores como alternativa ao uso do óxido de índio dopado com estanho (ITO) em células solares orgânicas. Os nanotubos foram dispersos e purificados em solução aquosa de dodecil sulfato de sódio (SDS) pelos processos de sonicação e centrifugação, e a dispersão monitorada por espectroscopia UV-Vis e potencial ?. Os nanocompósitos foram produzidos via polimerização in situ do monômero metacrilato de metila (MMA) na presença de 0 a 1% p/p NTCs e os filmes depositados através da técnica de revestimento por rotação a alta velocidade (spin coating). A reação de polimerização foi acompanhada pela calorimetria exploratória diferencial (DSC). Verificou-se que na presença de NTCs, a taxa de conversão do monômero é acelerada. A cinética de degradação térmica foi avaliada pelo método de Broido utilizando a análise termogravimétrica (TGA). Foi observado que os NTCs aumentam a estabilidade térmica do PMMA, retardando a degradação por despolimerização. Estudos por espectroscopia FT-IR mostraram uma banda de absorção em 1601 cm-1, (C=C), a qual não é característica do PMMA, indicando que os NTCs participam da polimerização do PMMA. Para concentrações de até 1% p/p de NTCs, os filmes PMMA/NTC apresentaram excelentes propriedades ópticas. Ou seja, baixo coeficiente de absorção, na ordem de 103 cm-1, altos valores de gap óptico (Eopt), entre 3,2 e 4,14 eV, e alta transparência por todo espectro visível, entre 88 e 93%. Nas mesmas concentrações, foi observada uma diminuição substancial na resistividade elétrica dos filmes em 8 ordens de grandeza (de 1016 para 108 ?/quadrado), comparados ao filme de PMMA puro. Entretanto, a faixa de resistividade alcançada ainda é típica de materiais isolantes. Estudos de otimização poderiam originar filmes PMMA/NTC como uma alternativa promissora para ITO em OPVs
Abstract: Carbon nanotubes (CNTs) have interesting features for applications in transparent electrodes. When dispersed at the nanoscale, they become transparent within the visible range and are able to conduct electricity after reaching the percolation threshold in an insulating polymer matrix. In this work, the use of multi-walled carbon nanotubes (MWCNTs) is described for the production of flexible transparent conducting polymer films as an alternative to the use of indium-tin oxide (ITO) in organic solar cells. The nanotubes were dispersed and purified in an aqueous solution of sodium dodecyl sulfate (SDS) by the process of sonication and centrifugation, and the dispersion monitored by UV-Vis spectroscopy and ? potential. The nanocomposites were produced via in situ polymerization of the monomer methyl methacrylate (MMA) in the presence of 0 to 1 %wt. of CNTs. The films were deposited by the spin-coating technique. The polymerization reaction was monitored by differential scanning calorimetry (DSC). It was found that in the presence of CNTs, the conversion rate of the monomer is accelerated. The kinetics of thermal degradation was measured according to the Broido's method by using thermogravimetric analysis (TGA). It was observed that CNTs increase the thermal stability of PMMA, slowing degradation by depolymerization. FT-IR data showed an absorption band at 1601 cm-1 (C = C), which is not characteristic of PMMA, indicating that the CNTs takes place in the polymerization of PMMA. For concentrations up to 1wt% of CNTs, the PMMA/CNT films had excellent optical properties, i.e., a low absorption coefficient in the order of 103 cm-1, wide optical gap (Eopt) between 3.2 and 4.14 eV, and high transparency within the whole visible range, between 88 and 93%. In the same concentrations, the electrical resistivity of the films dropped by 8 orders of magnitude (from 1016 to 108 ?/sqr), compared to the pure PMMA film. Even though this electrical resistivity value is typical of insulating materials, further optimization studies could provide PMMA/CNT films as a promising alternative to ITO in OPV
Mestrado
Ciencia e Tecnologia de Materiais
Mestre em Engenharia Química

碩士
南台科技大學
機械工程系
94
Acrylic(PMMA) has the best impact resistant, pressure resistant, and good optical properties, so it is applied in the optics lens, sunglasses or windscreen of transportation. Titanium nitride has the characteristic of the high hardness and high wear resistant, is often used as a protective coating for corrosion and wear. It is a barrier material kind of frequently used in semiconductor process. The purpose of this paper is deposition titanium nitride films by magnetron sputtering on PMMA. Hope that acrylic has better value. We deposited a layer of aluminum film between acrylic substrate and titanium nitride film first. The aluminum film has lower resistivity, and it is one of the materials of inter-layer that often be used. Try to improve the adhesion of the titanium nitride film and probe into influence of microstructure and mechanical properties of different thickness inter-layer of aluminum films to its titanium nitride films. In the experiment, we measured the deposition rate of aluminum film on PMMA and titanium nitride film on aluminum film by surface profiler (Alpha-step) first, and try to control the thickness of the aluminum films are 20nm, 40nm and 80nm, titanium nitride film is 80nm. The physical properties of the TiN/Al films are analyzed from AFM, SEM, XRD, mechanical properties are measured hardness of the films, and observation its change of the contact angle on the surface. As the results of experiments, we find the surface roughness and hardness of the films are increased as the films increased gradually. The contact angle is 105° while the inter-layer thickness of aluminum films are 40nm, surface structure will change from hydrophilic to hydrophobic. Besides, we find preferred orientation is changed into the TiN（111）trend from the TiN（200）. Key words : TiN/Al films, magnetron sputtering, contact angle, preferred orientation.

The use of thin-film techniques for the fabrication of microfluidic devices has gained attention over the last decade, particularly for three-dimensional channel structures. The reasons for this include effective use of chip volume, mechanical flexibility, dead volume reduction, enhanced design capabilities, integration of passive elements, and scalability. Several fabrication techniques have been adapted for use on thin films: laser ablation and hot embossing are popular for channel fabrication, and lamination is widely used for channel enclosure. However, none of the previous studies have been able to achieve a strong bond that is reliable under moderate positive pressures. The present work aims to develop a thin-film process that provides design versatility, speed, channel profile homogeneity, and the reliability that others fail to achieve. The three building blocks of the proposed baseline were fifty-micron poly(methyl methacrylate) thin films as substrates, channel patterning by laser ablation, and device assembly by thermal-fusion bonding. Channel fabrication was characterized and tuned to produce the desired dimensions and surface roughness. Thermal bonding was performed using an adapted mechanical testing device and optimized to produce the maximum bonding strength without significant channel deformation. Bonding multilayered devices, incorporating conduction lines, and integrating various types of membranes as passive elements demonstrated the versatility of the process. Finally, this baseline was used to fabricate a droplet generator and a DNA detection chip based on micro-bead agglomeration. It was found that a combination of low laser power and scanning speed produced channel surfaces with better uniformity than those obtained with higher values. In addition, the implemented bonding technique provided the process with the most reliable bond strength reported, so far, for thin-film microfluidics. Overall, the present work proved to be versatile, reliable, and fast, making it a good candidate to reproduce several on-chip functions. Future work includes implementing thick-substrate bonding techniques to further improve the process and decrease energy requirements.

The thermal conductivity of PMMA films with thicknesses from 5 to 50 nanometers and layered over a treated silicon substrate is explored numerically by the application of the reverse non-equilibrium molecular dynamics (NEMD) technique and the development of a coarse-grained model for PMMA, which allows for the simulation time of hundreds of nanoseconds required for the study of large polymer systems. The results showed a constant average thermal conductivity of 0.135 W/m_K for films thickness ranging from 15 to 50 nm, while films under 15 nm in thickness showed a reduction of 30% in their conductivity. It was also observed that polymer samples with a degree of polymerization equal to 25% of the entanglement length had 50% less thermal conductivity than films made of longer chains. The temperature profiles through the films thickness were as predicted by the Fourier equation of heat transfer. The relative agreement between the thermal conductivity from experiments (0.212 W/m_K for bulk PMMA) and the results from this investigation shows that with the proper interpretation of results, the coarse-grained NEMD is a useful technique to study transport coefficients in systems at larger nano scales.

博士
國立成功大學
微電子工程研究所碩博士班
98
The structure and electric characteristics of PMMA-based organic thin film transistor and their pentacene film grown on PMMA film have been investigated in this dissertation Four solvents, toluene, p-xylene, o-Dichlorobenzene, and chloroform were selected to dissolve PMMA and AFM was used to measure the grain size and roughness of pentacene grown on PMMA. Several material characterization techniques, such as X-ray diffraction (XRD), contact angle, X-ray photoelectron spectroscopy(XPS) and atomic force microscope (AFM) were performed to characterize the material quality. This study gave clear experimental evidence that the quality of pentacene grown on the PMMA dielectric layer dissolved in toluene is the best choice. The treatment of UV-ozone on ITO surface can reduces the leakage current through PMMA dielectric layer. With the UV-ozone cleaner treatment for ITO surface, the average number of pinholes in PMMA film deposited the ITO reduces from 47 to 19 (in 25 μm2 area). The leakage current density reduces from 1.5 to 2.0 × 10-2 A/m2. According to the analysis of XRD and AFM measurements, the optimum pentacene thickness grown on PMMA film was 60 nm. In this dissertation, we have also compared the performance of PMMA-based OTFTs with that of SiO2-based OTFTs, including pentacene film quality and electric characteristics. This study also gave clear experimental evidence that the quality of pentacene grown on the PMMA layer was better than that grown on SiO2 dielectric layer. XRD was used to measure the diffraction intensity in order to observe the crystalline quality of pentacene thin film on PMMA and SiO2. AFM was also used to measure the grain size and roughness of pentacene grown on PMMA and SiO2 and subsequently deduce a match in surface free energy between pentacene and PMMA. The maximum saturation field-effect mobility was 0.241 cm2/V s. It was also found that the electric characteristics of OTFT with PMMA dielectric layer were beter than that of OTFT with SiO2 dielectric layer. The excellent transfer characteristics of pentacene-based OTFTs with PMMA as dielectric layer were obtained: drain saturation current (3 μA at VGS = -50 V and VDS = -50 V), threshold voltage (VT = -11.5 V), on/off current ratio (7.7 × 104), and field-effect mobility (μsat = 0.48 cm2/Vs) were obtained by inserting the MoO3 buffer layer. The MoO3/pentacene interface was analyzed by XPS and found the C1s core level peak in MoO3/pentacene interface shifted to higher binding energy. For the energy barrier of 0.2 eV in Au/MoO3 interface, the carriers can sufficiently jump the energy barrier into MoO3 layer as VDS increases, and than efficiently inject into pentacene film. This is why the performance of OTFTs with MoO3 buffer layer can be enhanced as VDS is more than 1.7 V. Besides, the MoO3 buffer layer was also a protector against the penetration phenomena, which would cause interface dipole barrier. Therefore, excellent performance of pentacene-based thin film transistors will be achieved by inserting a MoO3 buffer layer.

碩士
國立中央大學
機械工程學系
101
Polymethylmethacrylate (PMMA), also called acrylic glass, is transparent, chemically stable, thermoplastic and inexpensive, making it suitable for many biochemical applications. Among different fabrication processes of PMMA such as gelation, injection and casting, plasma polymerization is the one capable of depositing nano scale films on almost any substrate uniformly and rapidly. In this study, we investigated the structure, composition, surface and mechanical properties of deposited PMMA films on glass by RF power plasma inside a vacuum chamber. The deposition was carried out under different RF power, working pressure and deposition time, from which an optimal fabrication condition was explored. On the characterization part, following tests were carefully conducted: the thickness (around 50 to 200nm) was estimated by surface profiler; microstructures was determined by Fourier transform infrared spectroscopy (FT-IR); surface chemical compositions were examined by X-ray photoelectron spectroscopy (XPS);surface morphology and roughness were measured by atomic force microscopy (AFM) and the wettability by water contact angle. Primary results showed that deposited films are physically and chemically stable for more than a week, which are readily available for hepatocytes cell culture, cell proliferation, cell activity and function execution test.

Magnetostrictive materials belong to an important class of smart magnetic materials which have potential applications as ultrasonic transducers, sensors, actuators, delay lines, energy harvesting devices etc. Although, magnetostrictive property is exhibited by almost all ferro and ferrimagnetic materials, the R-Fe type (R represents rare earth elements) intermetallic compounds display maximum promise owing to the large magnetostriction exhibited by them at ambient temperature. Among the several R-Fe type compounds, Tb-Fe and Sm-Fe alloys are found to exhibit maximum room temperature positive and negative magnetostriction respectively. Recently, Fe-Ga based alloys have gained significant interest as newly emerging magnetostrictive material due to a good combination of magnetic and mechanical properties. These magnetostrictive materials in thin film form are of interests for several researchers both from fundamental and applied perspectives. Currently, many researchers are exploring the possibility of using magnetostrictive thin films in micro- and nano-electromechanical systems (MEMS and NEMS). Three material systems viz. Fe-Ga, Tb-Fe and Sm-Fe in thin film form have been chosen for our investigations. DC magnetron sputtering and e-beam evaporation techniques were used for deposition of these thin films on Si (100) substrates. Several aspects such as evolution of microstructure, film surface morphology, structure and change in film composition with different processing conditions were investigated in detail, as the existing literature could not provide a clear insight. Further, detailed magnetic characterizations of these films were carried out and established a process-structure-property correlation. The thesis is divided into seven chapters. The first chapter presents a brief introduction of magnetostrictive phenomena and the physics behind its origin. A brief history of evolution of magnetostrictive materials with superior properties is also brought out. Introduction to the material systems considered for the present study has also been presented. Discussions on various aspects like crystal structures, magnetic properties, and phase diagrams of these material systems are also included in this chapter. Magnetostriction in thin films and its importance in current technological applications are discussed in short. Further, a summary of existing literature on thin films of these materials has been narrated to highlight the perspective of the work done in subsequent chapters. In addition to this, a clear picture of the grey area for further investigations has been provided. Formulation of detailed scope of work for this study is also provided in this chapter. Details of different experimental techniques used in this study for deposition and characterization of these films are given in chapter 2. In the third chapter of the thesis a detailed study on the structural, microstructural and magnetic properties of Fe-Ga films deposited using dc magnetron sputtering technique are presented. The effect of sputtering parameters such as (i) Ar pressure, (ii) sputtering power, (iii) substrate temperature and (iv) deposition time/film thickness on the magnetic properties of the films are discussed in detail. All the films are found to be polycrystalline in nature with A2 type structure as evidenced from grazing incidence X-ray diffraction (GIXRD) and transmission electron microscope (TEM) studies. Surface morphology of the films are found to be affected with processing conditions considerably. Thermomagnetic behaviour of the films studied using a Superconducting Quantum Interference Device (SQUID) magnetometer under zero field cooled (ZFC) and field cooled (FC) conditions are also presented. The sputtering parameters are also found to influence the magnetic properties of the films through modifications in microstructure, surface morphology and film compositions. Irrespective of the sputtering parameters, room temperature (RT) deposited Fe-Ga films are found to exhibit large magnetic coercively and large saturation magnetic field as compared to the bulk alloy of similar compositions which are not desirable for micromagnetic device applications. A significant improvement in the magnetic properties of the films was obtained in the films deposited at higher substrate temperatures and is correlated with modifications in grain size and film surface roughness. These films are also found to exhibit better magnetostriction than the RT deposited films. Further, the magnetic properties of Fe-Ga films as a function of film thickness in the range 2 – 480 nm are also presented. The nature of variation of coercively with film thickness was correlated with grain size effect and explained successfully with the help of random anisotropy model. In the fourth chapter, studies on the microstructural and magnetic properties of Tb-Fe films were presented. It was reported earlier that TbxFe100-x films exhibit in-plane magnetic anisotropy for the films with x > 42 at.% of Tb and out-of-plane anisotropy for the composition 28 < x < 42. Presence of these anisotropies is technologically important for different applications. We have studied the magnetic properties of Tb-Fe films in these two composition range. TbxFe100-x films with 54  x  59 were prepared using dc magnetron sputtering technique under varying Ar pressure and sputtering power and the details about microstructural and magnetic properties are presented in this chapter. All the films are found to be amorphous in nature. While the composition of the film is found to remain constant with sputtering power, the Fe concentration in the film is found to be depleted with increase in Ar pressure. Magnetic properties are found to change from superparamagnetic to ferromagnetic behaviour with increase in sputtering power. Curie temperature of the films are found to be low (below RT) and is explained based on sperimagnetic ordering of magnetic sub-lattices. The perpendicular magnetic anisotropy (PMA) or out-of-plane anisotropy behaviour of Tb-Fe films were not studied in detail as a function of film thickness. We have successfully prepared TbxFe100-x films with 29  x  40 using e-beam evaporation technique using alloy target composition of TbFe in order to study the PMA behaviour as a function of film thickness. The thickness of the films was varied from 50 to 800 nm. All the films are found to be amorphous and columnar growth structure with fine channels of voids are observed from the TEM studies. Detailed magnetization and thermomagnetic measurements were carried out using SQUID magnetometer at different temperatures. The out-of-plane magnetic coercivity of the films was found to increase with film thickness and then decreases with further increase in thickness. Maximum coercivity of ~ 20 kOe has been obtained for the 400 nm thick film. Magnetic domain patterns were studied using magnetic force microscopy (MFM) technique and the observed magnetic properties are correlated with domain pattern and microstructures. Although there are several reports on device applications of Sm-Fe thin films which exhibit negative magnetostriction, a comprehensive study on the effect of different process parameters on the magnetic properties and its correlation with structure and microstructure is still elusive. Hence, Sm-Fe films were deposited on Si (100) substrate using dc magnetron sputtering technique under varying Ar pressure and sputtering power. Effect of these parameters on the microstructural and magnetic properties of the films was studied in detail and is presented in chapter 5. The curie temperature of the films was found to increase with increase in sputtering power and Ar pressure. This was attributed to increase in film thickness and size of islands (atomic clusters). Coercivity as low as 30 Oe has been achieved in the film deposited at 15 mTorr Ar pressure. The Curie temperature for the films deposited at higher Ar pressure (10 and 15 mTorr) are found to be above RT. Maximum saturation magnetostriction of ~ - 390 -strains has been achieved in the film deposited at 15 mTorr Ar pressure. Rapid thermal processing (RTP) experiments were also carried out to increase the magnetic ordering in the films deposited at low Ar pressure (5 mTorr) by imparting structural ordering. Large improvement in magnetization and Curie temperature of the film was observed after RTA. However, this could be attributed to the formation of nano-crystalline Fe phase as evidenced from the TEM studies and thermomagnetic measurements. An overall summary of the experimental results has been presented in chapter 6. The scope of work for further study in future has also been highlighted in chapter 7.

Magnetostrictive materials belong to an important class of smart magnetic materials which have potential applications as ultrasonic transducers, sensors, actuators, delay lines, energy harvesting devices etc. Although, magnetostrictive property is exhibited by almost all ferro and ferrimagnetic materials, the R-Fe type (R represents rare earth elements) intermetallic compounds display maximum promise owing to the large magnetostriction exhibited by them at ambient temperature. Among the several R-Fe type compounds, Tb-Fe and Sm-Fe alloys are found to exhibit maximum room temperature positive and negative magnetostriction respectively. Recently, Fe-Ga based alloys have gained significant interest as newly emerging magnetostrictive material due to a good combination of magnetic and mechanical properties. These magnetostrictive materials in thin film form are of interests for several researchers both from fundamental and applied perspectives. Currently, many researchers are exploring the possibility of using magnetostrictive thin films in micro- and nano-electromechanical systems (MEMS and NEMS). Three material systems viz. Fe-Ga, Tb-Fe and Sm-Fe in thin film form have been chosen for our investigations. DC magnetron sputtering and e-beam evaporation techniques were used for deposition of these thin films on Si (100) substrates. Several aspects such as evolution of microstructure, film surface morphology, structure and change in film composition with different processing conditions were investigated in detail, as the existing literature could not provide a clear insight. Further, detailed magnetic characterizations of these films were carried out and established a process-structure-property correlation. The thesis is divided into seven chapters. The first chapter presents a brief introduction of magnetostrictive phenomena and the physics behind its origin. A brief history of evolution of magnetostrictive materials with superior properties is also brought out. Introduction to the material systems considered for the present study has also been presented. Discussions on various aspects like crystal structures, magnetic properties, and phase diagrams of these material systems are also included in this chapter. Magnetostriction in thin films and its importance in current technological applications are discussed in short. Further, a summary of existing literature on thin films of these materials has been narrated to highlight the perspective of the work done in subsequent chapters. In addition to this, a clear picture of the grey area for further investigations has been provided. Formulation of detailed scope of work for this study is also provided in this chapter. Details of different experimental techniques used in this study for deposition and characterization of these films are given in chapter 2. In the third chapter of the thesis a detailed study on the structural, microstructural and magnetic properties of Fe-Ga films deposited using dc magnetron sputtering technique are presented. The effect of sputtering parameters such as (i) Ar pressure, (ii) sputtering power, (iii) substrate temperature and (iv) deposition time/film thickness on the magnetic properties of the films are discussed in detail. All the films are found to be polycrystalline in nature with A2 type structure as evidenced from grazing incidence X-ray diffraction (GIXRD) and transmission electron microscope (TEM) studies. Surface morphology of the films are found to be affected with processing conditions considerably. Thermomagnetic behaviour of the films studied using a Superconducting Quantum Interference Device (SQUID) magnetometer under zero field cooled (ZFC) and field cooled (FC) conditions are also presented. The sputtering parameters are also found to influence the magnetic properties of the films through modifications in microstructure, surface morphology and film compositions. Irrespective of the sputtering parameters, room temperature (RT) deposited Fe-Ga films are found to exhibit large magnetic coercively and large saturation magnetic field as compared to the bulk alloy of similar compositions which are not desirable for micromagnetic device applications. A significant improvement in the magnetic properties of the films was obtained in the films deposited at higher substrate temperatures and is correlated with modifications in grain size and film surface roughness. These films are also found to exhibit better magnetostriction than the RT deposited films. Further, the magnetic properties of Fe-Ga films as a function of film thickness in the range 2 – 480 nm are also presented. The nature of variation of coercively with film thickness was correlated with grain size effect and explained successfully with the help of random anisotropy model. In the fourth chapter, studies on the microstructural and magnetic properties of Tb-Fe films were presented. It was reported earlier that TbxFe100-x films exhibit in-plane magnetic anisotropy for the films with x > 42 at.% of Tb and out-of-plane anisotropy for the composition 28 < x < 42. Presence of these anisotropies is technologically important for different applications. We have studied the magnetic properties of Tb-Fe films in these two composition range. TbxFe100-x films with 54  x  59 were prepared using dc magnetron sputtering technique under varying Ar pressure and sputtering power and the details about microstructural and magnetic properties are presented in this chapter. All the films are found to be amorphous in nature. While the composition of the film is found to remain constant with sputtering power, the Fe concentration in the film is found to be depleted with increase in Ar pressure. Magnetic properties are found to change from superparamagnetic to ferromagnetic behaviour with increase in sputtering power. Curie temperature of the films are found to be low (below RT) and is explained based on sperimagnetic ordering of magnetic sub-lattices. The perpendicular magnetic anisotropy (PMA) or out-of-plane anisotropy behaviour of Tb-Fe films were not studied in detail as a function of film thickness. We have successfully prepared TbxFe100-x films with 29  x  40 using e-beam evaporation technique using alloy target composition of TbFe in order to study the PMA behaviour as a function of film thickness. The thickness of the films was varied from 50 to 800 nm. All the films are found to be amorphous and columnar growth structure with fine channels of voids are observed from the TEM studies. Detailed magnetization and thermomagnetic measurements were carried out using SQUID magnetometer at different temperatures. The out-of-plane magnetic coercivity of the films was found to increase with film thickness and then decreases with further increase in thickness. Maximum coercivity of ~ 20 kOe has been obtained for the 400 nm thick film. Magnetic domain patterns were studied using magnetic force microscopy (MFM) technique and the observed magnetic properties are correlated with domain pattern and microstructures. Although there are several reports on device applications of Sm-Fe thin films which exhibit negative magnetostriction, a comprehensive study on the effect of different process parameters on the magnetic properties and its correlation with structure and microstructure is still elusive. Hence, Sm-Fe films were deposited on Si (100) substrate using dc magnetron sputtering technique under varying Ar pressure and sputtering power. Effect of these parameters on the microstructural and magnetic properties of the films was studied in detail and is presented in chapter 5. The curie temperature of the films was found to increase with increase in sputtering power and Ar pressure. This was attributed to increase in film thickness and size of islands (atomic clusters). Coercivity as low as 30 Oe has been achieved in the film deposited at 15 mTorr Ar pressure. The Curie temperature for the films deposited at higher Ar pressure (10 and 15 mTorr) are found to be above RT. Maximum saturation magnetostriction of ~ - 390 -strains has been achieved in the film deposited at 15 mTorr Ar pressure. Rapid thermal processing (RTP) experiments were also carried out to increase the magnetic ordering in the films deposited at low Ar pressure (5 mTorr) by imparting structural ordering. Large improvement in magnetization and Curie temperature of the film was observed after RTA. However, this could be attributed to the formation of nano-crystalline Fe phase as evidenced from the TEM studies and thermomagnetic measurements. An overall summary of the experimental results has been presented in chapter 6. The scope of work for further study in future has also been highlighted in chapter 7.

Research Doctorate - Doctor of Philosophy (PhD)
Graphene, a monolayer of graphite, has drawn a great deal of attention for organic electronic applications. Excellent optical transmittance combined with its extraordinary electrical properties makes it an attractive material for using as a transparent, conductive electrode in the fabrication of organic solar cells (OSCs). To bring graphene to mass production, synthesis methods are required for its growth as a large-area film. Chemical vapour deposition (CVD) is a novel technique proposed to produce high quality, large-area graphene films. Recently, the use of copper as a catalyst for graphene growth has been more popular compared with other metals since the carbon solubility in copper is much lower, allowing better control over the number of graphene layers. Here, we report optimisation of graphene growth on two different copper substrates - copper foil and thin copper film - at low temperatures (below 500 °C) using poly(methyl methacrylate) (PMMA) as a carbon source. It was found that the 140 °C heated precursor promotes the growth of a mono-layer graphene, while the 400 °C heated precursor results in multi-layer graphene. For optimisation, three different temperature parameters, including the annealing temperature of the copper substrates (Tanneal), precursor temperature (Tprecursor) and growth temperature (Tgrowth), have been identified and independently studied. Firstly, the optimal Tanneal of the copper substrates prior to graphene deposition was required to be sufficiently high (> 900 °C) to cause the recrystallisation of large Cu grains in the substrate surface. Secondly, Tprecursor needs to be high enough to produce volatile precursor fragments which subsequently decompose on the catalyst surface. In the case of PMMA, this requires Tprecursor > 140 °C. Finally, Tgrowth has to be sufficiently high to activate carbon diffusion and rearrangement on the catalyst surface. Particularly, this temperature needs to be at least 450 °C for a Cu foil catalyst. By working at the Tanneal of 900 °C, it was also found that the Cu foil substrate annealed for 10 minutes under hydrogen flow rate of 100 sccm and the thin Cu film substrate annealed for 1 hour under hydrogen flow rate of 50 sccm were the optimal annealing conditions. A pre-thermal annealing study of the copper substrates was undertaken to examine the change of structural and morphological properties. In this study, it was found that the substrates have a good nanocrystalline cubic structure, dominated by (100) with the crystallize size of ~ 200 nm and (111) planes with the crystallite size of ~ 100 nm for the Cu foil and the thin Cu film, respectively. This treatment also showed that the hydrogen reducing gas effectively removes the copper oxide impurities. Moreover, the samples annealed beyond 900 °C have a smooth surface morphology with uniform coverage and grain sizes ~ 1.3 and ~ 88 µm for thin Cu film and Cu foil, respectively. The annealed copper substrates were further used as catalysts for growing graphene. By working at a growth temperature of 450 °C, the graphene growth time on the Cu foil catalyst and the thickness of thin Cu film catalyst were also optimised, and were found to be 1 minute and 500 nm, respectively. The transmittance of graphene films resulting from the growth on both of the substrates was above 85%. However, their electrical properties were significantly different; the lowest sheet resistances obtained were 1.2 and 14.0 kΩ/ for the graphene growth on the Cu foil and thin Cu film catalysts, respectively. These results are much higher compared to the best reported Rsheet for single-layer graphene (ca.350 kΩ/) [1-3]. For the processed graphene/graphite films used as a transparent, conductive electrode for fabricating OSC devices, they demonstrated working devices with PCEs of between 0.07 - 0.36 %. The low PCEs of the fabricated devices were due to the high sheet resistance (a few kΩ/sq) of these device electrodes.

碩士
輔仁大學
化學系
90
The photochrome of azobenzene dye will induce trans-cis photoisomerization under ultra-visible light﹒The reverse reaction will be reverse by heat or light with different wavelength；Moreover , there are three properties : 1. Good arrangement of polymer , 2. Good solvation , 3. Good process to be drived easily , which can be applied in storage material of light in this kind of copolymer﹒Therefore , it is quite potential and valuable to do further research﹒ This research is to synthesize monomer with azobenzene and copolymerize with methyl methacrylate (MMA)﹒Then the copolymer will become side-chain copolymer﹒The optical property of this copolymer is worthy of research﹒In this study, the azobenzene moiety was attached with the same electron-withdrawing group and the same spacer length(n=11)﹒Further , we synthesize azobenzene and copolymerize with different mole percentage of MMA to induce copolymerizing reaction﹒The copolymer we get after reaction will be discussed individually in the following two situations:1. Solvent polarity；2. Thin film and studied it`s phenomenon of photochrome﹒I would suggest that each kind of phenomenons in the copolymer are affected by different solvent polarity and their application in the storage material of light in practice﹒The study result shows that photochrome wil isomerizes faster with higher mole percentage of azobenzene in the copolymer﹒However, the rate of isomerization will be faster with higher solvent polarity due to more attractions﹒

碩士
崑山科技大學
機械工程研究所
96
The nano technology has been advanced continuously recent years. The micro-wearing behavior and mechanism of thin film material under micro/nano scale have discussed. The most research are discuss the properties of nano-tribology and the manufacturing process technology which sputtering on the PMMA substrate. The properties of nano-wearing experiments are measured by NanoTest and Pin-On Disc (POD), respectively. The experimental parameters are: applied load, rotational speed and rotational radius, etc. And analyze the surface morphology under wearing behavior, to create the rule which the mechanical properties after coat film for future research. As the experimental results, the average coefficient of friction can be separated two stages: firstly, due to the adhesion effect phenomenon occurred on the surface of metal thin film when the loading is around 1 to 5mN; second is the ploughing causing the coefficient of friction increased when the loading between 20 to 200mN. The stick-slip phenomenon occurred simultaneously under large loading, it’s the special phenomenon which due to the substrate effect when the metal film coated on the PMMA substrate.

碩士
國立中山大學
物理學系研究所
91
The laser-induced holographic gratings in the Azo dye-doped PMMA thin films with liquid crystal were investigated by changing the temperature of the sample, the angle of two writing beams and the rubbing. The high power Q-switch pulse laser has been used as the writing beams and the He-Ne cw laser has been used as a real-time probe beam to detect the first order diffraction singals. The grating are the results of photo-isomerization of azo dye and diffusions of liquid crystal. The model has been established to analyze the first order diffraction signals in order to understand the mechanism of grating and the effect of temperature and angle.

碩士
國立成功大學
材料科學及工程學系
103
The effects of solvent affinity and mixing ratio in solutions on phase separation behavior of a binary blend system of poly(3-hexylthiophene- 2,5-diyl)(P3HT) and poly(methyl methacrylate)(PMMA) have been explored. The solvent affinity was found critical for the precipitation sequence of dissolved components during spin coating, which provides the background to elucidate the occurrence of vertical phase separation. The morphologies of horizontal phase separation are dominated by the mixing ratios of these two immiscible constituents. Upon obtained results, both vertical and horizontal phase separation are able to be manipulated comprehensively for achieving the needed distribution of semiconductive conjugated polymers within thin film. Furthermore, the growth of thicker fibrous P3HT crystals was found when sufficient P3HT/PMMA interfacial areas were established by the resultant morphology of phase separation, which has not been unveiled before.

碩士
國立虎尾科技大學
光電工程系光電與材料科技碩士班
104
This study will be used polymethyl methacrylate (acrylic) as the substrate, by plasma enhanced chemical vapor deposition system (PECVD), thermal evaporation system, RF magnetron co-sputtering system, and spray painting, testing and adhesion improvement on a functional thin film that include hard coatings thin film, reflection thin film, anti-Glare Coating and transparent conductive thin film. The results showed that when the functional thin film adhered to the acrylic substrate only 0B degree level, in order to improve the adhesion of the functional thin film on the acrylic substrate using PECVD deposition of the organic silicon thin film as a buffer layer for the purpose of enhancing the adhesion of the functional thin film between the acrylic substrate and to reduce the residual stress after the thin film deposition, the degree of adhesion level reaches 5B, then through the force of 100 mN flannel friction 1000 times, hydrochloric acid and brine environmental testing to explore the functional thin film for improving results under harsh environment stability. In order to analyze the reasons of the improvement on the thin film, and using a surface profiler measurement of curvature before and after the thin film deposition, and then calculate for residual stress via Stoney equation, when the residual stress is smaller the better adhesion of the thin film.Using Fourier transform infrared spectroscopy measure thin film chemical bonding, and analyze attachment relationship with the homogeneity of material.X-ray diffraction measure the crystallinity of the thin film, the thin film is attached to the analysis of the crystalline degree of influence.Measuring the contact angle that the thin film surface hydrophilic and hydrophobic, hydrophilic and hydrophobic for analysis of the impact on attachment.Measured using an atomic force microscope roughness of the thin film, analyze the relationship between roughness and adhesion.

by Lui Bong Chun, Richard.
Thesis (M.Phil.)--Chinese University of Hong Kong, 1995.
Includes bibliographical references.
Abstract
Acknowledgment
Chapter Chapter 1 --- Introduction --- p.1
Chapter 1.1 --- Background for the Project --- p.1
Chapter 1.1.1 --- Interests in Blue-Green Laser --- p.1
Chapter 1.1.2 --- Progress of Blue-Green Laser --- p.2
Chapter 1.2 --- The Aim of the Project --- p.3
Chapter 1.3 --- Overview the Remaining Parts of this Thesis --- p.4
Chapter 1.4 --- References --- p.6
Chapter Chapter 2 --- Sum Frequency Generation --- p.8
Chapter 2.1 --- Introduction --- p.8
Chapter 2.2 --- Sum Frequency Generation --- p.8
Chapter 2.2.1 --- Theoretical Background for Sum Frequency Generation --- p.9
Chapter 2.2.2 --- The Coupled Wave Equations for SFG --- p.13
Chapter 2.2.3 --- Phase Matching Considerations --- p.16
Chapter 2.3 --- References --- p.18
Chapter Chapter 3 --- Cerenkov Radiation --- p.19
Chapter 3.1 --- Introduction --- p.19
Chapter 3.2 --- The Properties of Cerenkov Radiation by Using TM Mode --- p.21
Chapter 3.2.1 --- Refractive Index Notation --- p.23
Chapter 3.2.2 --- Fundamental Wave TM Guides Mode --- p.23
Chapter 3.2.3 --- Second Harmonic TM Radiation Mode --- p.24
Chapter 3.2.4 --- Efficiency of SHG --- p.25
Chapter 3.3 --- Simplified Model Analysis of Cerenkov Radiation in TE Mode --- p.29
Chapter 3.4 --- Simulation --- p.33
Chapter 3.4.1 --- Modeling the LiNb03 --- p.33
Chapter 3.4.2 --- Modeling an Asymmetric Slab Waveguide ´ؤPMMA doped with MNA on Fused Quartz --- p.37
Chapter 3.4.3 --- Modeling a Symmetric Slab Waveguide ´ؤPMMA doped with MNA on Fused Quartz --- p.42
Chapter 3.5 --- References --- p.47
Chapter Chapter 4 --- Ellipsometry --- p.49
Chapter 4.1 --- Introduction --- p.49
Chapter 4.2 --- General Principles --- p.49
Chapter 4.3 --- Basic Operation --- p.50
Chapter 4.4 --- The Optical Constants of the Bulk Materials --- p.51
Chapter 4.5 --- Calculation the Refractive Index of the Substrates --- p.53
Chapter 4.6 --- Ellipsometric Theory for the Thin Film --- p.57
Chapter 4.7 --- Measurement the Refractive Index and the Thickness of the Thin Film --- p.59
Chapter 4.7.1 --- Data --- p.62
Chapter 4.7.2 --- Discussions --- p.73
Chapter 4.8 --- Calculation the Refractive Index of the thin Film by Considering as a Bulk Material --- p.78
Chapter 4.9 --- References --- p.80
Chapter Chapter 5 --- Prism Coupling --- p.81
Chapter 5.1 --- Introduction --- p.81
Chapter 5.2 --- Coupling of a Plane Wave --- p.82
Chapter 5.3 --- Numerical Approach for the Calculation of the Coupling Efficiency --- p.85
Chapter 5.4 --- Experiment --- p.88
Chapter 5.4.1 --- Experimental Setup --- p.88
Chapter 5.4.2 --- Experimental Result and Discussions --- p.90
Chapter 5.5 --- References --- p.92
Chapter Chapter 6 --- Conclusion --- p.93
Chapter Chapter 7 --- Future Plans --- p.96
Chapter 7.1 --- Simplified Model of Corona Poling --- p.96
Chapter 7.2 --- Advanced Models of Poling --- p.98
Chapter 7.2.1 --- Slab Waveguide --- p.98
Chapter 7.2.2 --- Channel Waveguide --- p.99
Chapter 7.3 --- References --- p.100
Chapter Appendix 1 --- Materials' Descriptions --- p.A-l
Chapter A.1.1 --- 2-Methyl-4-Nitoaniline --- p.A-1
Chapter A.1.2 --- Poly ( Methyl Methacrylate ) --- p.A-3
Chapter A.1.3 --- References --- p.A-4
Chapter Appendix 2 --- Fabrication Procedures --- p.A-5
Chapter A.2.1 --- Cleaning the Apparatus --- p.A-5
Chapter A.2.2 --- Cleaning the Substrate --- p.A-5
Chapter A.2.3 --- Thin film Fabrication --- p.A-5
Chapter A.2.4 --- Thin Film Removal --- p.A-6
Chapter A.2.5 --- References --- p.A-6
Chapter Appendix 3 --- Alpha Step --- p.A-7
Chapter A.3.1 --- Introduction --- p.A-7
Chapter A.3.2 --- Experimental Setup --- p.A-8
Chapter A.3.3 --- Experimental Results --- p.A-9
Chapter A.3.3.1 --- Thin Film of PMMA without Dopant --- p.A-9
Chapter A.3.3.2 --- Thin Film of PMMA doped with MNA --- p.A-19
Chapter A.3.4 --- Discussions --- p.A-27
Chapter A.3.5 --- References --- p.A-28
Chapter Appendix 4 --- Scanning Electron Microscope --- p.A-29
Chapter A.4.1 --- Scanning Electron Microscope --- p.A-29
Chapter A.4.2 --- Reference --- p.A-30
Chapter Appendix 5 --- Gaussian Beam & Coordinate System Transformation --- p.A-31
Chapter A.5.1 --- Gaussian Beam in a Homogeneous Medium --- p.A-31
Chapter A.5.2 --- Transformation of the Coordinate Systems --- p.A-32
Chapter A.5.3 --- Reference --- p.A-32
Chapter Appendix 6 --- Waist Size Measurement of Gaussian Beam --- p.A-33
Chapter A.6.1 --- Waist Size Measurement of Gaussian Beam --- p.A-33
Chapter A.6.2 --- References --- p.A-34
Chapter Appendix 7 --- Quasi Phase Matching --- p.A-35
Chapter A. 7.1 --- Introduction --- p.A-35
Chapter A.7.2 --- Basic Concept of QPM --- p.A-36
Chapter A.7.3 --- References --- p.A-38
Chapter Appendix 8 --- Program Listing --- p.A-41
Chapter A.8.1 --- Program Listing ( Chapter 3 ) --- p.A-41
Chapter A.8.1.1 --- Program 3.1 (transcendental.m ) --- p.A-41
Chapter A.8.1.2 --- Program 3.2 (linbo3.m) --- p.A-42
Chapter A.8.2 --- Program Listing ( Chapter 4 ) --- p.A-45
Chapter A.8.2.1 --- Program 4.1 ( ellipsometry.m ) --- p.A-45
Chapter A.8.3 --- Program Listing ( Chapter 5 ) --- p.A-47
Chapter A.8.3.1 --- Program 5.1 ( parameter.m ) --- p.A-47
Chapter A.8.3.2 --- Program 5.2 ( coupling.m ) --- p.A-49
Chapter A.8.3.3 --- Program 5.3 ( v_3_amp.m ) --- p.A-50
Chapter A.8.3.4 --- Program 5.4 ( input_profile.m ) --- p.A-51