Dissertations / Theses on the topic 'Films sol-gel'

This thesis presents a study of the mechanical properties of thin films. The main aim was to determine the properties of sol-gel derived coatings. These films are used in a range of different applications and are known to be quite porous. Very little work has been carried out in this area and in order to study the mechanical properties of sol-gel films, some of the work was carried out on magnetron sputtered metal coatings in order to validate the techniques developed in this work. The main part of the work has concentrated on the development of various bending techniques to study the elastic modulus of the thin films, including both a small scale three-point bending, as well as a novel bi-axial bending technique based on a disk resting on three supporting balls. The bending techniques involve a load being applied to the sample being tested and the bending response to this force being recorded. These experiments were carried out using an ultra micro indentation system with very sensitive force and depth recording capabilities. By analysing the result of these forces and deflections using existing theories of elasticity, the elastic modulus may be determined. In addition to the bi-axial bending study, a finite element analysis of the stress distribution in a disk during bending was carried out. The results from the bi-axial bending tests of the magnetron sputtered films was confirmed by ultra micro indentation tests, giving information of the hardness and elastic modulus of the films. It was found that while the three point bending method gave acceptable results for uncoated steel substrates, it was very susceptible to slight deformations of the substrate. Improvements were made by more careful preparation of the substrates in order to avoid deformation. However the technique still failed to give reasonable results for coated specimens. In contrast, biaxial bending gave very reliable results even for very thin films and this technique was also found to be useful for determination of the properties of sol-gel coatings. In addition, an ultra micro indentation study of the hardness and elastic modulus of sol-gel films was conducted. This study included conventionally fired films as well as films ion implanted in a range of doses. The indentation tests showed that for implantation of H⁺ ions at doses exceeding 3x10¹⁶ ions/cm², the mechanical properties closely resembled those of films that were conventionally fired to 450°C.

Este trabalho experimental trata da caracterização de filmes sol-gel por elipsometria. A caracterização é um procedimento importante na determinação das propriedades físico-químicas de qualquer material como, por exemplo, filmes finos sol-gel. É possível produzir materiais de natureza diversa (vítreos, cerâmicos e cristalinos) pela técnica sol-gel. A elipsometria, por sua vez, é uma técnica recente na determinação do índice de refração complexo de um material. Os seus fundamentos teóricos tratam da natureza da luz polarizada e sua propagação através de um sistema ótico. No decorrer do trabalho, estes princípios possibilitarão descrever os sistemas óticos utilizados na parte experimental. Os filmes finos têm propriedades óticas e mecânicas que podem diferir bastante daquelas encontradas em certo volume do material. A análise das suas propriedades é feita através das medidas dos seguintes parâmetros: espessura, índice de refração e perfil de tensões. Um dos objetivos deste trabalho foi à observação da evolução das propriedades óticas e mecânicas durante o processo de densificação. Os filmes caracterizados são de sílica (SiO2), depositados sobre três tipos de substratos: vidro comum, sílica fundida, e silício. A caracterização deste material durante o processo de densificação térmica é dividida nas seguintes etapas: a) evolução estrutural através da medida da espessura, b) análise das porosidades pelo espectro do índice de refração, c) determinação das tensões. Como conseqüência, a montagem de um microelipsômetro que mede retardações óticas de filmes finos fez-se necessária e foi realizada durante este trabalho. A sua calibração é possível pela técnica de elipsometria nula. Assim sendo, pode-se especificar o equipamento, bem como aplicá-lo em diversas situações como: a) determinação do estado tênsil ou compreensivo de filmes de CeO2-TiO2; b) determinar tensões em filmes de sílica, c) análise de defeitos em filmes de um óxido misto de SnO2 In2O3(ITO).
This is an experimental work about the characterization of thin sol-gel films by ellipsometry. The characterization is an important procedure on determining the physical-chemical properties of many materials such as thin films produced by the sol-gel process. It is possible to produce several kinds of materials (vitreous, ceramic and crist.alline) by using the sol-gel process. The elipsometry, itself is a new technique for the determination of the complex refractive index of a material. Its theoretical principles concern about the nature of the polarized light, and its propagation through an optical system. These principles will be used to describe the optical systems of the experimental procedure along this work. The thin films have optical and mechanical properties that can strongly differ from those found for the material at bulk form. The analwses of these properties is carried out by the measurement of the following parameters: thickness, refractive index and stress profile. One of the goals of this work is to observe the evolution of the optical and mechanical properties during the densification process. The characterized films are of silica (SiO2) deposited on three kinds of substrate: ordinary glass, vitreous silica and single crystal silicon. The characterization of this material during the densification process is divided in t.he following steps: a ) structural evolution by thickness mesurement; b ) porosity study by refractive index spectrum; c) stress determination. As a consequence of this characterization, it was constructed, along the work, a microellipsometer which measures thin film retardation. Its calibration is possible by using the null ellipsometry technique. In this way, the equipment can be specified and applied to different situations such as: a) determination of the stress or compressive state for CeO2-TiO2; b ) stress measurements of silica films; c ) defect st.udy of ITO films SnO2 In2O3.

Sol-gel derived silica coatings were deposited on soda-lime-silica by dip-coating. An absorbing metallic layer was sputtered onto the surface of the gel to couple near-infrared radiation from a Nd:YAG laser into the transparent coating. Laser energy was utilized to heat the ceramic coating on a substrate which has a lower glass transition temperature than the coating. Scanning the sample across the beam's path resulted in the formation of a 50 mum wide channel. The characteristics of a channel were altered by varying laser power, sol-gel coating thickness, and scanning speeds. Profilometry and SEM analysis verified that the coating can be heated to high temperatures without damaging the substrate.

This thesis describes the development and characterisation of dye sensitised Inorganic:Organic (10) heterojunction photovoltaic (PV) cells of the form Au/MPc/TiO2/InSnO2 or F-SnO2 (where MPc= copper phthalocyanine, chloroaluminium phthalocyanine or lead phthalocyanine). The transparent TiO2 films were prepared by Sol-Gel techniques and characterised optically, structurally and electrically. The effects of and interactions between Sol-Gel process parameters have shown that the parameters undergo significant interaction with particular effects on the TiO2 film thickness and thickness related properties obtained during dip coating. The film refractive index n was in the range 2.73-1.81 and wavelength dependent. The conductivity of the films derived from Au/TiO2/InSnO2 structure was 4.26x10[-6]S/cm. E[0] varied from 3.4-3.35eV where delta=2 indicting an indirect allowed transition in 1 layer thick films to E[0] ~3.2eV where delta=3 indicating indirect forbidden transition as the number of coating layers increased. The spectral response, dark and illuminated J(V) and dark C(V) characteristics of the dye sensitised 10 PV cells have been determined. Spectral response indicates that all of the organic dyes studied can be used to sensitise Sol-Gel derived TiO2 into the visible region Corresponding photovoltaic and junction parameters were derived. Photovoltaic effects were observed in all devices studied, however cell efficiencies were poor, in the range (eta~0.0001-0.046%). The low quantum efficiencies were anticipated to be a consequence of the presence of recombination centres at the TiO2/MPc heterointerfaces and the high observed series resistance due to the low conductivity of the MPc films. The MPc/TiO2 junction formed a rectifying contact. C(V) analysis indicated that the junction was electrically abrupt. The dark J(V) characteristics were divided into three regimes, (i) A reverse bias regime in which the device acts as a p-n heterojunction, (ii) an intermediate forward voltage regime, where the derived values of m > 2 indicating the presence of a high density of interface states (iii) High forward regime. All devices deviate from the standard diode equation as a consequence of space charge effects in the organic layer, the ideality factors m"2. Temperature dependence measurements of PbPc/TiO2 heterojunctions show that the junction currents are a composite of tunnelling and recombination. PV cell parameters were influenced by changes in ambient conditions, the thickness of organic layers and variations in incident intensity. The J[sc] and V[oc] were proportionally and logarithmically dependent on the incident intensity respectively. The high R[s] is believed to be responsible for the poor cell efficiencies reducing FF, J[sc] and eta. A 30 fold increase in eta was observed when the organic film thickness was reduced from 500nm to 100nm. Exposure to atmosphere reduced eta and is likely to be a consequence of O2 trapping centres. The work has demonstrated the feasibility of a low cost solid state 10 heterojunction photovolatic cell. However improvements in efficiency are required to produce a commercially viable device.

L’étude menée concerne divers aspects d’une nouvelle voie de synthèse sol-gel : la génération électro-assistée de films à base de silice fonctionnalisée et/ou mésostructurée, ainsi que leurs applications en électrochimie analytique. Des films à base de silice fonctionnalisée par des groupements amine ou thiol ont été déposés sur électrode d’or par catalyse électrochimiquement assistée de la polycondensation. La formation d’une monocouche auto-assemblée partielle de mercaptopropyltriméthoxysilane permet une très bonne adhésion du film silicaté sur la surface d’or. Le processus d’électro-dépôt est caractérisé par deux étapes successives de vitesse différente. A une étape de dépôt lent et régulier succède une croissance bien plus rapide du film. L’utilisation des électrodes modifiées a été envisagée en tant que capteur de Cu2+. En introduisant un tensioactif dans le sol de synthèse, il est possible d’électrogénérer des films à base de silice mésoporeuse de structure hexagonale avec les pores orientés perpendiculairement par rapport au substrat (difficile à obtenir par d’autres méthodes). Il semblerait que l’électrochimie permette à la fois un contrôle de la structure du tensioactif à la surface de l’électrode et la croissance simultanée du film sol-gel. Cette méthode d’électrogénération permet aussi d’obtenir des films fins homogènes sur des surfaces non planes ou présentant des hétérogénéités de conductivité. Enfin, une approche préliminaire a été proposée visant à appliquer le processus d’électrogénération, couplé à la technique de microscopie électrochimique à balayage, pour déposer localement des films à base de silice sous forme de plots de taille micrométrique sur or
The study deals with various aspects of a novel method of sol-gel synthesis : the electro-assisted generation of functionalized and/or mesostructured silica thin films, and their applications in analytical electrochemistry. Sol-gel-derived silica films functionnalized with amine or thiol groups have been electrogenerated on gold electrodes. The formation of a partial self-assembled monolayer of mercaptopropyltrimethoxysilane (MPTMS) on gold led to a silica film adhering well to the electrode surface owing to the MPTMS acting as a « molecular glue ». The whole process was characterized by two successive distinct rates, starting by a slow deposition stage leading to thin deposits, which was followed by a much faster film growing in the form of macroporous coatings. The use of these modified electrodes was considered as a voltammetric sensor for copper(II). By adding a surfactant in the synthesis medium, it’s possible to electrogenerate mesostructured silica films with hexagonal structure with pore channels oriented perpendiculary to the substrate (which is difficult to get by other methods). The electrochemically-induced-self-assembly of surfactant-templated silica thin films can be applied to various conducting supports. The broad interest of the novel method was demonstrated by its ability to produce homogeneous deposits of silica on non-planar surfaces or heterogeneous substrates, what is difficult by the traditional techniques of film deposition. Finally, a preliminary approach has been proposed in order to apply the electrodeposition process coupled with a scanning electrochemical microscope in order to get localized sol-gel deposits at the micrometric size level on gold

In this study, maghemite (&
#947
-Fe2O3) thin films were prepared by chemical solution deposition on glass and quartz substrates. The solution was prepared by using 0.3 M iron (III) nitrate [Fe(NO3)3 - 9H2O] as precursor and dissolved in a mixture of 2-methoxyethanol and acetylacetone in a molar ratio of 20:2, by stirring the solution at RT for 2 hours. Substrates were prepared by either piranha etching method or ultrasonic cleaning method. The solution was spin coated on glass and quartz substrates at 1400 and 4000 rpm for 1 minute. The resultant film thickness was found as 65 and 80 nm by SEM. Viscosity of the main solution was found to be approximately as 0.0035 Pa.s by viscosity measurement. TGA/DTA analyses showed that, to produce maghemite thin film, heat treatment should be done between 330 °
C and 440 °
C. Homogeneous and crack free maghemite thin films were observed by Energy Dispersive Spectrometry (EDS) and Scanning Electron Microscope (SEM) methods. TEM studies verified maghemite thin film formation by using electron diffraction and SAED (selected area electron diffraction) method. Thin film characteristics were evaluated by changing the experimental parameters which are annealing temperature, annealing time and thickness of the films using XRD (x-ray diffraction) method. Optical band gap of maghemite thin films were found as approximately 2.64 eV by UV-VIS Spectrophotometer. Magnetic properties of maghemite thin films were also examined by VSM (vibrating sample magnetometer).

Magnetite (Fe3O4) thin films were prepared by a sol-gel process in which, a solution of iron (III) nitrate dissolved in ethylene glycol was applied on glass substrates by spin coating. Xerogel films were obtained by drying the coated films at 110 °
C. The films were sintered between 300 °
C and 450 °
C in order to observe the phases existing in the films at different temperatures. Coating solution showed Newtonian behaviour and viscosity was found as 0.0215 Pa.s. DTA analysis showed that, sintering temperature should be selected between 291 °
C and 350 °
C in order to produce magnetite thin films. Prepared magnetite thin films were characterized by XRD, SEM, AFM, TEM, VSM and UV-Vis spectrometer. In-plane grazing angle diffraction studies showed that magnetite phase was present upon sintering the films at 300 °
C. From the SEM studies, it was shown that films with defect free surfaces were obtained and by cross section studies, thickness of the films was found as ~10-200 nm. AFM images showed that no cracks or any other defects on the film surface were present. TEM results proved the existence of single phase magnetite in the produced films. UV-Vis spectrum results showed that transmittance of the films increases with decreasing sintering temperature and increasing spinning rate. Up to 96% transmittance was observed between the wavelengths of 900-1100 nm. Magnetic properties of magnetite thin films were also examined by VSM (Vibrating Sample Magnetometer) and ferromagnetic behaviour was shown using VSM data.

Ferroelectric perovskite thin films for voltage tunable applications, namely (Ba,Sr)TiO3 (Barium Strontium Titanate or BST) and (Pb,Sr)TiO3 (Lead Strontium Titanate or PST), are synthesized via the so-called sol-gel route. While BST shows the tendency to severe film cracking, PST can be grown crack free onto platinised Si standard substrates and even directly onto SiO2, SiNx or bare Si. The growth kinetics of PST on platinised SiO2/Si and directly on SiO2/Si are studied in detail using X-ray diffractometry (XRD), scanning electron and atomic force microscopy, SEM and AFM respectively. It is shown that PST begins to crystallise at 500°C on Ti/Pt and 550°C directly on SiO2. After a thermal treatment of 650°C for 15 min both films are fully crystallised with random (100) and (110) orientation and a smooth surface. The dielectric properties, e.g. dielectric constant, loss and tunability, of PST 50/50 are measured using a standard Ti/Pt bottom electrode with Cr/Au top electrodes and a TiW/Cu bottom electrode on which the PST thin film was bonded with TiW/Cu top electrodes. The Cu/PST/Cu system shows an enhanced performance in terms of loss resulting in a larger device quality factor and a figure of merit (FOM) of 18.25 compared to 16.6 for the configuration using a Pt bottom electrode. The maximum tunability is 73% with an applied voltage of 35V and the dielectric constant at zero bias is ~ 420 with a loss < 4 %. (Pb0.4Sr0.6)(MnxTi1-x)O3 (Mn doped PST 40/60) thin films with x = 0, 0.01, 0.03, and 0.05 are grown on Ti/Pt coated SiO2/Si substrates. The surface morphologies, dielectric and tunable properties of these films are investigated as a function of Mn content (x). It is found that the grain size/roughness, dielectric constant, loss, tunability and figure of merit are affected by the Mn doping level. Further on it is found that the ferroelectricity and the transition temperature between the cubic paraelectric and tetragonal ferroelectric state increase with Mn content. The dielectric constant at zero bias reaches a maximum of 1100 and the maximum FOM is 23.96 with 3 mol% Mn; whereas the maximum value of the tunability is 76.72% at 10 V with 1 mol% Mn. A detailed understanding of the effect of Mn doping is developed and presented. It is found and explained that a doping level of 2 mol% Mn results in optimal properties in terms of tunability and loss. Auger spectroscopy is used to study the compositional change in the interfacial region between PST and PZT thin films and SiO2/Si substrates to understand the growth kinetics of PST directly onto SiO2 in more detail. The thin films from both materials are annealed under the same conditions (temperature and time). It is found that strontium stops the lead diffusion into SiO2 by forming SrSiO3/Sr2SiO4 and/or SrO, maintaining a well defined SiO2 region, while PbSiO3 is formed in the PZT/SiO2 system. It is shown that SrO covalently saturates all Si dangling bonds by forming SrSiO3 and/or Sr2SiO4. This provides the necessary ionic template towards the perovskite SrO-terminated SrTiO3, on which PST can grow further on. A single layer of PST is finally used as a buffer layer for the growth of piezoelectric PZT directly onto SiO2 to replace the common Ti/Pt bottom electrode. The initial characterisation of PZT device structures shows that PZT films with PST as a diffusion buffer had fully crystallized in the perovskite phase exhibiting good dielectric and ferroelectric behaviour. Although the piezoelectric coefficients of the PZT films were not measured directly in this study, it is envisaged from the experimental data of the dielectric constant and hysteresis loop that the PZT/PST composite has the potential to provide good and comparable piezoelectric performances as typically observed in PZT device structures grown on commonly used Ti/Pt.

The goal of this research was the fabrication of thin films with magneto-optic (MO) properties. Accomplishment of this task was achieved via sol-gel processing of rare-earth and aluminum substituted yttrium-iron garnet (RxY3-xAlyFe5-yO12, R,Al:YIG), where R= Bi, Gd, Er, Ho. Detailed are the processing conditions, parameters and results leading to R,Al:YIG films with MO response. Success was attained with a 0.25M Gd,Al:YIG solution spin coated for 120 seconds at 3500rpm onto a (111) gadolinium gallium garnet (GGG) substrate and calcinated at 900°C for 4 hours. Samples were characterized via x-ray diffraction (XRD), magneto-optical loop tracer, scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), profilometry and optical microscopy.
Master of Science

Mestrado em Ciência e Engenharia de Materiais
Dielectric, piezoelectric and ferroelectric thin films have been in the past years significantly studied because of their technological interest in a wide range of applications in the microelectronics industry. Among the several ferroelectric materials, compositions within the solid solution between the ferroelectric BaTiO3 and the quantum paraelectric SrTiO3 (Ba1-xSrx)TiO3 (BST), possess high dielectric constant and relatively low loss over a wide frequency range (till >1 GHz), low-leakage current density, a large electric field dielectric tunability and a composition dependent Curie temperature. These properties make BST thin films attractive for high density dynamic random access memories (DRAMs), and low cost agile microwave circuits, such as phase shifters, tunable filters, tunable matching network and high tuning frequency range voltage controlled oscillators. Moreover BST is a lead free perovskite making it an ideal material from the environmental point of view. These applications require the growth of high quality BST thin films, in addition to fundamental understanding of their structural and dielectric properties, which often diverge from those in equivalent bulk material. The high temperatures required for the crystallization of the perovskite BST films are not compatible with Si based large scale integrated circuits. SiO2 and/or metal silicides formation occurs when BST is deposited on silicon at temperatures above 700ºC. An underlying silicide layer reduces materials high dielectric permittivity, since silicide has lower permittivity than the perovskite oxide, reducing the film effective capacitance. At these high temperatures recrystallization of the electrode layer beneath the film (e.g. platinum layer) may occur, which can lead to hillock formation and electrical shorting of BST films. Moreover, thermal stresses generated at high temperatures might affect the long-term reliability of the device. Hence the improvement and optimization of the processing conditions of BST thin films as well as the development of low temperature processes for the fabrication of BST films are still a key aspect from the technologic point of view. Additionally, a low annealing temperature is also essential when metallic or glass substrates are required. The present master thesis addresses the investigation on the preparation of BST thin films by sol gel at temperatures lower than 700ºC. Sol-gel derived (Ba0.8Sr0.2)TiO3 thin films with improved dielectric properties were prepared at 600°C, on Pt/TiO2/SiO2/Si substrate through the use of diphasic precursor sols. BST nanometric powders were dispersed in the amorphous BST precursor sol to prepare the diphasic precursor sol and (Ba0.8Sr0.2)TiO3 thin films without and with 1 mol%, 5 mol% and 10 mol% (Ba0.8Sr0.2)TiO3 seeds were fabricated. The role of seeds was investigated and analyzed on the crystalline phase evolution, microstructure development and electrical properties of BST thin films. The improvement on the characteristics of seeded BST films when compared with unseeded films was highlighted by a comprehensive structural, microstructural and electric characterization of the films. It was shown that using perovskite BST nanopowders as seeds results in the crystallization of a single perovskite phase in BST films either at lower temperatures or at shorter annealing time when compared with the preparation of identical films without seeds. The presence of nano sized BST seeds in the film precursor sol lowers the barrier for BST nucleation and results in a high density of small crystallites in the film. XRD analysis showed that the temperature at which the perovskite phase is formed (or identified) was decreased from 650ºC to 550ºC when BST seeds were used in the precursor sols and the temperature at which the pure perovskite phase is obtained was decreased from 700ºC to 600ºC. The seeded BST films exhibit enhanced crystllization kinetics and the overall activation energy for the perovskite crystllization was reduced from 189 kJ/mol for the unseeded film to 86 kJ/mol for 1 mol% seeded BST film and to 80 kJ/mol for 5 mol% seeded film. Scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM) were employed to characterize the influence of seeds on the crystallinity, structure, microstructure, morphology and interface between BST thin films and the substrate. Both SEM and AFM surface morphology results showed that the grains of seeded films were smaller, more homogeneously distributed than unseeded ones. The surface roughness of BST films measured by AFM was decreased by the presence of BST nano seeds. TEM analysis clearly revealed that the crystallinity of BST films was enhanced with the presence of BST seeds under the same annealing conditions. The dielectric properties of BST thin films, including permittivity, loss tangent, tunability of the dielectric constant were evaluated and discussed as a function of seeds content. The dielectric constant of unseeded films annealed at 600ºC for 30 hours in oxygen were improved by the addition of 5 mol% seeds from ~300 to 400 at 1kHz, respectively. Simultaneously, the dissipation factors were decreased by the presence of 5 mol% seeds from ~0.1 to 0.07 at 1 kHz, from 0.07 to 0.01 at 1 MHz, respectively. The presence of 5 mol% seeds improved the tunability of BST films and an increment from 52% to 65% at 6 V was observed for unseeded and 5 mol% seeded BST thin films annealed at 600ºC for 30 hours in oxygen. The leakage current density of BST films with 5 mol% seeds heat treated at 600ºC for 30 hours in oxygen is 0.95×10-7 A/cm2 up to the applied voltage of 2.33 V (97 kV/cm), which was improved when compared with 0.88× 10-7 A/cm2 up to 2.02 V (84 kV/cm) measured for BST films without seeds. The value of the leakage current of both unseeded and 5 mol% seeded films meet the requirements for G-Byte DRAMs. Identically to the rest of the electrical properties, the polarization versus electric field (P-E) hysteresis was improved by the introduction of seeds. The remnant polarization Pr of BST films with 5 mol% seeds was 3.55 μC/cm2 with a coercive field of 75 kV/cm, which was considerably enhanced when compared with 1.8 μC/cm2 for BST films without seeds with a coercive field of 50 kV/cm. Corroborating the above results, piezo force microscopy (PFM) of BST seeded and non seeded thin films demonstrated the improved ferroelectric properties of BST films prepared with nanometric seeds.
Filmes finos dieléctricos, piezoeléctricos e ferroeléctricos têm sido muito estudados no passado recente, por causa do interesse tecnológico relacionado com a gama alargada de aplicações destes materiais na indústria microelectrónica. De entre os vários materiais ferroeléctricos, as composições pertencentes à solução sólida composta pelo ferroeléctrico BaTiO3 e o quantum paraléctrico SrTiO3, (Ba1-xSrx)TiO3 (BST), possuem constantes dieléctricas elevadas e baixas perdas dieléctricas até frequência elevadas (>1 GHz), baixas densidade de correntes de fuga, elevada sintonabilidade da permitividade dieléctrica com o campo eléctrico e temperatura de Curie dependente da composição. Estas propriedades tornam os filmes finos de BST atractivos para dispositivos de memórias dinâmicas de acesso aleatório DRAMs, e de circuitos sintonizáveis às frequências das microondas (phase shifters, tunable filters, tunable matching network and high tuning frequency range voltage controlled oscillators). Por outro lado BST é um material livre de chumbo o que o torna ideal do ponto de vista ambiental para estas aplicações. As aplicações acima mencionadas requerem o fabrico de filmes finos de BST de elevada qualidade, juntamente com o entendimento das relações entre a sua estrutura e propriedades, que muitas vezes divergem das propriedades apresentadas pelos materiais equivalentes na forma de monolitos. As elevadas temperaturas necessárias para a cristalização de fase de perovesquite em filmes finos de BST não é compatível com a integração em larga escala em circuitos à base de silício. A formação de SiO2 e ou silicietos metálicos ocorre quando BST é depositado sobre silício a temperaturas elevadas acima de 700ºC. Camadas subjacentes de silicietos reduzem a elevada permitividade dieléctrica relativa do material, já que estes silicietos têm permitividade dieléctrica relativa inferior à do óxido perovesquítico. A estas temperaturas elevadas pode ocorrer a recristalização do eléctrodo colocado sob o filme (por exemplo platina), o que origina o aparecimento de curto circuitos nos filmes de BST. Mais ainda, as tensões térmicas geradas às temperaturas elevadas podem afectar a longo prazo o desempenho e a fiabilidade do dispositivo. Assim o melhoramento e optimização das condições de fabrico de filmes finos de BST, bem como o desenvolvimento de metodologias de processamento destes filmes a temperaturas mais baixas continua a ser um aspecto chave do ponto de vista tecnológico e de comercialização destes materiais. Acrescente-se que um processamento a baixas temperaturas é ainda essencial quando é necessária a utilização de substratos metálicos ou de vidro. A presente tese descreve a investigação conduzida na preparação de filmes finos de BST por sol gel a temperaturas inferiores a 700ºC. Filmes finos de (Ba0.8Sr0.2)TiO3 (BST80/20) com propriedades melhoradas foram preparados por sol gel a 600°C, sobre substratos de Pt/TiO2/SiO2/Si, através da utilização de soles precursores difásicos. Partículas nanométricas de BST foram dispersas em soles precursores de BST e filmes finos de BST80/20 sem e com 1 mol%, 5 mol% and 10 mol% de sementes de BST foram fabricados. O papel das sementes foi investigado e analisado na formação de fases, desenvolvimento microestrutural e propriedades dieléctricas dos filmes de BST. O estudo sistemático da estrutura, microestrutura e propriedades evidenciou as melhorias das características dos filmes de BST sementados. Foi mostrado que a utilização de partículas nanométricas de BST como sementes resulta na cristalização da fase pura de perovesquite nos filmes de BST ou a temperaturas mais baixas ou para tempos mais curtos. A presença de nanopartículas de BST nos soles precursores dos filmes baixa a barreira enérgica para a nucleação da fase de perovesquite de BST e origina no filme uma densidade elevada de pequenas cristalites. As análise de difracção de raios X mostraram que a temperatura à qual a fase de perovesquite se forma decresceu de 650ºC para 550ºC quando se utilizam sementes de BST nos soles precursores e que a temperatura à qual a fase pura de perovesquite é obtida decresceu de 700ºC para 600ºC. Os filmes sementados de BST exibem uma cinética de cristalização optimizada e a energia de activação para a cristalização da fase de perovesquite foi reduzida de 189 kJ/mol para os filmes não sementados para 86 kJ/mol e 80 kJ/mol para os filmes sementados com 1 mol% e 5 mol% de sementes, respectivamente. Para caracterizar a influência das sementes na estrutura, grau de cristalinidade, microestrutura, morfologia e interface filme / substrato foram utilizadas as técnicas de microscopia electrónica de varrimento (SEM), microscopia de força atómica (AFM) e microscopia electrónica de transmissão (TEM). Os resultados da morfologia da superfície dos filmes obtidos quer por SEM quer por AFM mostraram que os grãos dos filmes sementados são claramente menores e apresentam uma distribuição mais homogénea, relativamente aos filmes não sementados. A rugosidade da superfície dos filmes quantificada por AFM decresceu por adição das sementes. As análises de TEM revelaram que a cristalinidade dos filmes sementados é superior relativamente aos filmes não sementados, para filmes preparados em idênticas condições. As propriedades dieléctricas dos filmes finos de BST, que incluem a permitividade dieléctrica relativa, a perda dieléctrica, a sintonabilidade da permitividade dieléctrica foram avaliadas e analisadas em função do teor de sementes. A permitividade dieléctrica relativa de filmes não sementados e tratados termicamente a 600ºC durante 30 horas em oxigénio variou de ~300 para 400 a 1 kHz, pela adição de 5 mol% de sementes. Simultaneamente a perda dieléctrica decresceu para os filmes com 5 mol% de sementes de ~0.1 para 0.07 a 1 kHz e de 0.07 para 0.01 a 1 MHz. A presença de sementes melhorou a sintonabilidade dos filmes de BST, verificando-se um incremento de 52% para 65% a 6 V para os filmes sementados com 5 mol% de sementes em relação aos filmes não sementados ambos tratados termicamente a 600ºC por 30 horas em oxigénio. A densidade de corrente de fuga variou de 0.88 × 10-7 A/cm2 até uma voltagem aplicada de 2.02 V (84 kV/cm) para os filmes de BST não sementados e tratados termicamente a 600ºC durante 30 horas em oxigénio, para 0.95 ×10-7 A/cm2 até uma voltagem aplicada de 2.33 V (97 kV/cm) para filmes de BST com 5 mol% de sementes preparados nas mesmas condições. Os valores de densidade de corrente de fuga dos filmes sementados cumprem os requisitos estipulados por exemplo para as memórias dinâmicas de acesso aleatório (DRAM) de capacidade da ordem de G-Bytes. De forma idêntica à restante caracterização eléctrica, a presença de sementes em filmes de BST melhorou sua a resposta histerética da variação da polarização com o campo (P-E). Foram determinados valores de polarização remanescente de 3.55 μC/cm2 com campos coercivos de 75 kV/cm para filmes com 5mol% de sementes, valores estes consideravelmente superiores aos valores determinados para filmes não sementados de 1.8 μC/cm2 e 50 kV/cm para a polarização remanescente e o campo coercivo, respectivamente. Suportando os resultados anteriores, a microscopia de força piezoeléctrica (PFM) demonstrou igualmente a melhoria das propriedades ferroléctricas dos filmes de BST preparados com sementes.

L'utilisation de couches minces photocatalytiques à base de TiO2 est restreinte aux applications en extérieur ou sous lumière artificielle. En effet, ces systèmes nécessitent des UV pour être actif. Pour s'affranchir de ce point, plusieurs axes de travail ont été étudiés. Le premier consiste à utiliser un matériau différent de TiO2, absorbant dans le visible et ayant une activité significative. Nous avons pour cela développé un procédé de broyage original permettant d'étudier des poudres synthétisées sous forme micronique, dans des conditions semblables aux systèmes de référence. Une autre voie est de doper TiO2 avec de l'azote, de façon à modifier son spectre d'absorption dans le visible. Pour cela, nous avons mis au point un protocole permettant d'une part de nitrurer des nanoparticules à haute température (jusqu'à 900 °C) en conservant leur taille, ou d'autre part de nitrurer directement les couches à base de TiO2. Nous avons étudié les espèces apparues lors de la nitruration, leur impact sur l'activité des systèmes photocatalytiques à 390 nm. Nous avons alors pu mettre au point des couches 20 fois plus actives que les films de référence à cette longueur d'onde. Le dernier axe abordé consiste à associer TiO2 à un matériau absorbant dans le visible, et capable de transférer son excitation dans TiO2 : WO3. Ceci a nécessité l'étude des transferts électroniques entre les deux matériaux, par le biais d'une technique originale de voltamétrie. Nous avons alors pu utiliser ces mesures pour prédire les activités photocatalytiques. Cette méthode pourra être utilisée pour étudier d'autres hétérostructures, pouvant se montrer beaucoup plus actives.

A novel approach to sol-gel thin film fabrication has been developed which leads to the production of ultrathin ∼2 nm to 100 nm thick silica and conductively-doped silica films on metal and semiconductor substrates. The research described herein focuses on the development, characterization and potential application of these thin films in current technology. These ultrathin films were fabricated by a sol-gel procedure, which utilized highly diluted silica precursor compounds. The [H₂O]:[Si] ratio ranged from 50 to 1000, far above the typical values (4-10) used in sol-gel film preparation. This dilution leads to highly densified silica when spin-cast onto an appropriately compatible surface. The surface examined included Si(111)/SiO₂; ITO; and 3-(mercaptopropyl)trimethoxysilane (3MPT) modified Au and Ag. These surfaces must act as wetting control agents for the sol-gel precursor, while simultaneously providing adhesion to the nm sized sol-gel aggregates. The 3MPT-Ag monolayer was examined in detail by Tl, Pb and Cd underpotential deposition electrochemistry, to understand the interfacial structure of the molecule. These results show that the 3MPT monolayer is very stable to outside influences (i.e. Tl and Pb reversibly deposit monolayers at the metal surface). The UPD of metal ions is highly size dependent with Tl depositing with fewer kinetic limitations than Pb and Cd not depositing at all. Raman spectral characterization shows that 3MPT undergoes some reversible rearrangement during the UPD process. The electronic properties of the pure silica films were examined in great detail. The results suggested that in solution, a solvated gel layer at the film-solution interface gives rise to an anomalously low capacitance <100 pF/cm², which has no comparison in the current literature. In the dry state, these silica films have a dielectric constant of ε = 3.5, which is close to that of thermally-grown silica on silicon (3.9). These films were doped with 1,1'-bistriethoxysilylferrocene, an electrochemically-active sol-gel material. The results suggest that under the proper precursor solution conditions, thin ( <10 nm), uniform films can be fabricated. By simply adjusting the ratio of the ferrocene moiety in solution, the film composition can be adjusted. XPS verifies that the atom ratio in solution is near to the observed atom ratio in the films, with some indication of surface segregation of the ferrocene moiety. Electrochemical analysis of these films suggests that electron hopping between the ferrocene centers drives the electrochemical response only when there are pinhole defects, to support counterion conduction to the surface. (Abstract shortened by UMI.)

Nanotechnology is an exciting modern research field encompassing the traditionally specialist disciplines of chemistry, physics and engineering. Optics and catalysis are two areas of application that will continue to benefit from the recent improvements in control of materials morphology at the nano-scale. The work presented in this thesis is focussed on the application of the Sol-Gel technique in the realization of thin inorganic layers containing metal and semiconductor nanoparticles that are capable of reversibly of detecting gas phase analytes. Three synthetic approaches were adopted, each of them characterized by a systematic increase of the final materials morphology, structure and micro-structure control. This materials engineering was essential in order for nanocomposites with the desired optical and chemical properties applicable to gas sensing devices to be obtained. The synthesized layers comprised of an inorganic porous matrix (SiO2, TiO2 and NiO) containing nanosized metal (Au, Pt) or semiconductor crystals (NiO), and were shown to be active materials for chemical recognition of H2 and CO. The films were readily deposited onto different sensing supports, leading to successful gas detection via optical, conductometric and surface acoustic wave interfaces. SiO2-NiO-Au systems are capable to selectively detect H2 using an optical interface thanks to a marked wavelength dependence of its sensitivity toward this specie. However, if a peculiar NiO-Au morphology is obtained inside the SiO2 support CO is more likely to be detected. TiO2-Au thin films are shown to be excellent conductometric sensors for H2 detection, and ideal gas-sensing dynamics have been observed in this case. This class of layers demonstrated to be effective also for H2 detection through a Surface Acoustic Wave (SAW) interface. Monolayers of Au nanoparticles covered by a thin NiO layer showed promising sensing dynamics in the optical recognition of H2. In this case the material synthesis allows for a detailed control of the single nanocomposite constituents, thus opening the possibility for a finer tuning of the sensor sensitivity.

Ce travail de thèse s'inscrit dans la problématique de la préparation et l'intégration des matériaux diélectriques poreux à très faible permittivité (ULK) dans les interconnexions des puces microélectroniques. Cette étude porte sur le développement de couches minces hydrophobes ULK à porosité organisée et isolée, préparées par voies sol-gel et PECVD. Elle vise une amélioration des propriétés mécaniques et une diminution de la diffusion de polluants au cœur des films. Des matériaux hydrophobes mésostructurés et ULK (k < 2,2) ont ainsi été obtenus par voie sol-gel, après retrait d'un porogène par traitement thermique, ou pour la première fois sous UV. Les caractéristiques mésostructurales et microstructurales des couches ont été reliées aux caractéristiques de porosité et aux propriétés mécaniques. Les mesures électriques et de perméation de gaz de ces matériaux sont également discutées en vue de leurs applications en tant que matériaux ULK ou comme membranes de séparation de gaz. En PECVD, des matériaux polymère plasma à base de styrène ont été synthétisés et également caractérisés en termes de propriétés mécaniques et de séparation de gaz
This thesis is dealing with the challenging preparation and integration of porous dielectric materials with ultra low permittivity (ULK) for interconnections in microelectronic devices. This study focuses on synthesis of hydrophobic ULK thin layers with ordered and isolated porosity obtained by sol-gel. An improvement in mechanical properties and a decrease of the impurities migration in the heart of the bulk are expected. Hydrophobic and mesostructured ULK (k < 2.2) materials have been obtained by sol-gel after removal of porogen mesophases by thermal treatment and for the first time under UV irradiation. Mesostructural and microstructural properties of the layers were discussed with regard to the porosity and mechanical properties. The electrical and gas permeation measurements were also discussed in the framework of their possible applications as ULK materials and gas separation membranes, respectively. Using PECVD, styrene-based polymers, have been synthesized and also characterized in terms of mechanical and gas separation properties

Este trabalho apresenta resultados da preparação e caracterização de filmes finos de pentóxido de nióbio (Nb2O5) dopados com isopropóxido de zircônio (IV) Zr[O(CH2)2CH3]4, obtidos via processo sol-gel. A adição do precursor dopante teve como finalidade estudar a sua influência sobre as propriedades eletroquímicas destes filmes. Os sóis destinados à deposição destes filmes foram preparados a partir da mistura de pentacloreto de nióbio (NbCl5 anidro), n-butanol e ácido acético e sua submissão à ação de irradiação ultrasônica. A obtenção das camadas delgadas de Nb2O5:Zr, com diferentes espessuras (1 a 6 camadas), sobre um substrato de vidro recoberto com camada condutora eletrônica (ITO), fez-se pelo processo sol-gel juntamente com a técnica de imersão vertical (dip-coating). Os filmes foram submetidos a um tratamento térmico entre 450ºC e 560ºC, em atmosfera de ar, por 5 e 10 minutos. O estudo efetuado revelou que estes filmes finos de Nb2O5:Zr, apresentaram influência de concentração de zircônio, número de camadas e tempo de tratamento térmico nas propriedades eletroquímicas. As medidas de voltametria cíclica demonstraram que o processo de inserção/extração é reversível, enquanto medidas cronoamperométricas, demonstraram que o processo de intercalação atinge o seu valor máximo (35 mC/cm2) em 30s à -1,8V, para filmes dopados numa razão molar de 0,5% e com 5 camadas e tratamento térmico de 450°C por 10 minutos. Estes filmes também apresentaram nas análises microscópicas por MEV uma morfologia muito uniforme, lisa e sem rachaduras. Além disso, foi comprovada por análises EDX a presença de zircônio nos filmes. Todos estes resultados mostraram que os filmes de Nb2O5:Zr são promissores e excelentes candidatos à substituir filmes de WO3.em aplicações eletroquímicas.
This work consists of the preparation and characterization of niobium (V) oxide films (Nb2O5) doped with zirconium (IV) isopropoxide Zr[O(CH2)2CH3]4, was obtained by sol-gel process. The main objective of dopant addition was to study its influence on eletrochemical properties of these films. The sols used to deposition of these films were prepared from the mixture of niobium (V) (NbCl5), butanol and acetic acid by ultrasonic radiation action. The obtaining of the thin layers of Nb2O5:Zr with different thick (from 1 to 6 layers), on a glass substrate recovered with conductor layer ( ITO) was carried out by sol - gel process and dip-coating technique. The films were subjected to a thermal treatment between 450ºC and 560ºC, during some minutes in air atmosphere for 5 and 10 minutes. The study performed showed that these thin films of Nb2O5:Zr, presented influence of zirconium concentration, numbers of layers and time of termic treatment in the electrochemical properties. The measures of cyclic voltammetry showed that the process of insertion and extraction is reversible whereas the chronoamperometry measures showed the intercalation process has as maximum values (35mC/cm2) in 30s at -1,8V to doped films in a molar ration of 0,5% and with 5 layers and termci treatment of 450oC for 10 minutes. These films also presented in microscopic analysis by SEM a morphology very consistent, smooth and without cracks. Besides, it was proved by analysis by EDX the zirconium presences in the fims. All these results showed that the films of Nb2O5:Zr are promising and excellent application to replace films of WO3 in electrochemical application.

Des revêtements antiréflectifs hydrophobes à bas indice de réfraction ont été synthétisés sous forme de couches minces nanométriques de silice mésoporeuses par chimie sol gel couplée à un procédé de dépôt par dip coating sur substrats polymériques thermosensibles de polyméthacrylate de méthyle (PMMA) et de triacétate de cellulose (TAC). Les couches minces de silice pure et hybride ont été durcies par traitement en vapeur d’ammoniaque (TVA) à température ambiante. Les propriétés optiques, mécaniques et de résistance chimique des revêtements ont été optimisées et des mécanismes décrivant les modifications de la structuration induit par TVA selon la composition chimique des films ont été proposés grâce à l’étude de l’influence des conditions et des temps de traitement en vapeur d’ammoniaque. La condensation et la stabilisation de vapeur d’eau à l’intérieur de films de silice mésoporeux hydrophobes à l’aide de vapeur d’alcool ont été réalisées à température et pression ambiantes. L’étude de l’influence de la chimie de surface, de la taille des pores ainsi que des pressions partielles en eau et alcool, et de la nature du co-adsorbant alcoolique a permis de mettre en lumière les mécanismes d’adsorption et de confinement d’eau dans des nano-cavités hydrophobes. La diffusion d’eau à l’intérieur de monolithes de xérogel de silice millimétriques a été rapportée en utilisant pour la première l’ellipsométrie environnementale in situ. Des sujets aussi variés que la réalisation de films à gradient de fonctionnalité, la fabrication d’actuateurs sensibles à l’humidité à partir de films minces inorganiques, la synthèse de couches minces mésostructurées de BaTiO3 et la mise de forme 3D de films de quartz sont discutés dans ce manuscrit
Low refractive index hydrophobic antireflective coatings were synthetized as mesoporous nanometric thin silica films by use of sol gel chemistry coupled with the dip coating process on thermo sensitive polymeric substrates such as poly(methyl methacrylate) (PMMA) and cellulose triacetate (TAC). Thin films of pure and hybrid silica were stiffened by ammonia vapor treatment (AVT) at room temperature. Optical, mechanical and chemical stability of those coatings were optimized and the AVT-induced mechanisms of structuration depending on the chemical composition of silica films were proposed after the study of the influence of the ammonia treatment conditions and duration. Alcohol-assisted water vapor condensation and stabilization in hydrophobic mesoporous silica thin films were displayed at room temperature and atmospheric pressure. Study of the influence of surface chemistry and pore size, as well as partial vapor pressure of water and alcoholic co-adsorbant, and chemical nature of the alcohol allowed us to determine the mechanisms of water adsorption and confinement in hydrophobic nano-cavities. Water diffusion into millimetric scaled silica xerogel monoliths was reported using in situ environmental ellipsometry for the first time. Other subject as different as the production of graded functional films, fabrication of inorganic thin films based humidity sensitive actuators, synthesis of BaTiO3 mesostructured thin films and shaping of 3D quartz films are also discussed

This thesis presents an experimental study of the incorporation and optimization of sol-gel processed aluminum doped zinc oxide (AZO) thin films in solar cell devices. I first optimized the optoelectronic properties of AZO thin films by manipulating the dopant incorporation, choice of precursor chemicals and post deposition anneal treatments. Results showed that improved performance could be attributed to several factors, including improved charge carrier concentration, mobility and conductivity. AZO thin films with transmittance of over 90% and resistivity values of the order of 10-2 Ω•cm have been achieved. I also demonstrated the successful application of these AZO thin films in organic photovoltaics (OPV), to serve as an alternative to ITO electrodes. I demonstrated greater than 2-fold improvement in device efficiency through the modification of the front contact/polymer interface using zinc oxide buffer layers. This improved the charge selectivity of the electrodes and energy level alignment at the interface while reducing the recombination of separated charges and the device's series resistance. Finally, I showed that the efficiency of inverted ZnO/PbS quantum dots solar cells can be enhanced by optimizing the p-type PbS thickness, UV treating the n-type ZnO layer and exposing the devices in the dark to nitrogen. Both ZnO and AZO systems were studied, and efficiency enhancement were demonstrated for a range of Al content from 0 to O.4at.%.

Methyl-functionalized porous silica is of considerable interest as a low dielectric constant film for semiconductor devices. The structural development of these materials appears to affect their gelation behaviors and impact their mechanical properties and shrinkage during processing. 29Si solution NMR was used to follow the structural evolution of MTMS (methyltrimethoxysilane) polymerization to gelation or precipitation, and thus to better understand the species that affect these properties and gelation behaviors. The effects of pH, water concentration, type of solvents, and synthesis procedures (single step acid catalysis and two-step acid/base catalysis) on MTMS polymerization were discussed. The reactivity of silicon species with different connectivity and the extent of cyclization were found to depend appreciably on the pH value of the sol. A kinetic model is presented to treat the reactivity of both silicon species involved in condensations separately based on the inductive and steric effects of these silicon species. Extensive cyclization in the presence of acid, which was attributed to the steric effects among numerous reaction pathways for the first time, prevents MTMS gelation, whereas gels were obtained from the two-step method with nearly random condensations. The experimental degree of condensation (DC) at the gel point using the two-step procedure was determined to be 0.86, which is considerably higher than that predicted by the current accepted theories. Both chemical and physical origins of this high value were suggested. Aerogels dried by supercritical CO2 extraction were characterized by FTIR, 13C and 29Si solid-state NMR and nitrogen sorption. The existence of three residual groups (Si-OH, Si-OCH3, and Si-OC2H5) was confirmed, but their concentrations are very low compared to silica aerogels. The low concentrations of the residual groups, along with the presence of Si-CH3, make MTMS aerogels permanently hydrophobic. To enhance applicability, MTMS aerogels were successfully prepared that demonstrated shrinkage less than 10% after supercritical drying; proving that the rigidity of the gel network is not the sole factor, suggesting in the literature, to cause the huge shrinkage in many hybrid aerogels reported. An important finding of this work is that MTMS aerogels can be prepared without tedious solvent exchange and surface modification if the molar ratio of water/MTMS increases to 8, substantially reducing the cost of aerogel production. This result was attributed to MTMS's fully condensation and low concentrations of ring species.

This research explores new processing methods to decrease residual stress in ceramic films on metallic substrates, and thus to prevent large-scale cracking in the films. The system of particular concern is alumina-based ceramic coating on aluminum alloy, wherein coefficient of thermal expansion (CTE) of the ceramic is about 3x smaller than that of the alloy. The specific goal was to achieve relatively thick (~0.2mm) and substantially low density of cracks in dielectric films of alumina-based ceramic on aluminum alloy AA5052, by Chemically Bonded Composite Sol-Gel (CB-CSG) process. The principal strategies undertaken in the materials process engineering involved: (i) multi-layer film deposition - to introduce the intermediate steps of stress relaxation; (ii) composite sol-gel slurries with bi-modal particle size distribution - to decrease the overall process temperature, and to decrease film strain during thermal treatment as well as to increase the density and stability of the slurries; (iii) chemical bonding of the film through phosphating - to further decrease the process temperature to the level of 300°C; and (iv) introduction of organic-phase (citric acid) derived bond coats at the interface between the AA5052 substrate and the ceramic coating -to achieve residual stress relaxation through viscoelastic deformation of the bond coat. The coatings were processed through spray deposition of consecutive -40 µm thick layers, heat-treated at 300°C for 10 min after each deposition. Two size fractions of alumina powders (average size of 0.5 µm of "fine" and 3 µm of "coarse") were used in formulation of the Composite Sol-Gel (CSG) slurry, and the fine/coarse particle content was optimized based on slurry viscosity and stability, as well as properties of the final coating. The coatings were characterized for microstructure, residual stresses and dielectric strength, as a function of the process parameters. The most important finding of this work is that it is possible to deposit thick ceramic films on aluminum alloy substrates, if all four processing strategies listed above are implemented simultaneously. In particular, the citric acid - derived organo-ceramic bond coats seem to play an important role in relaxing residual stresses resulting from differential thermal contraction and expansion. It is concluded that the viscoelastically deforming organo-ceramic bond coat helps to relax residual stresses in the coating layers due to differential thermal contraction/expansion, and thus allows deposition of films of up to 200 µm thickness. Dielectric strength of the CB-CSG alumina coated AA5052 aluminum reached a maximum of 15±1 kV/mm for the first layer, and subsequently decreased to 10.5±1 kV/mm. It is believed that this decrease in the dielectric strength after the first layer is caused by increased density of cracks in the coating, as evidenced by decrease of the residual stress in the coatings.
Applied Science, Faculty of
Materials Engineering, Department of
Graduate

Wide bandgap semiconductors have been broadly investigated for their potential to detect and emit high energy ultraviolet (UV) photons. Advancements in deep UV optoelectronic materials would enable the efficient and affordable realization of many medical, industrial and consumer UV optical devices. The traditional growth method, vacuum deposition, is an extremely complicated and expensive process. Sol-gel processing dramatically simplifies facility requirements and can be scaled to industrial size. The work presented here involves a novel study of the ternary wide bandgap material Ni1-xMgxO. Films were developed by sol-gel spin coating for investigation of material and electrical properties. This method produced films 200-600 nm thick with surface roughness below 4 nm RMS. Sintered films indicated an improvement from 60% to 90% transmission near the band edge. Additionally, compositional analysis was performed by X-ray Photoelectron Spectroscopy and film defects were characterized by photoluminescence using a continuous wave He-Cd UV laser, revealing the expected oxygen defect at 413nm. This film growth technique has produced thin polycrystalline films with low surface roughness and a high degree of crystalline orientation; crucial characteristics for semiconductor devices. These films have demonstrated the ability to be tuned over the full compositional range from the bandgap of NiO (3.6 eV) to that of MgO (7.8 eV). Optoelectronic devices produced by standard photolithographic techniques are discussed as well as the electrical transport properties of their metal contacts. Based on initial results, these films have demonstrated strong potential as solar blind detectors of UV radiation.
B.S.E.E.
Bachelors
Engineering and Computer Science
Electrical Engineering

Thesis (M.A.)--Boston University PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.
Periprosthetic infections are a major complication of joint replacement and other orthopedic surgeries. The majority of these infections are caused by S. aureus which, when they grow on an implant, develop into a bacterial biofilm. The bacterial biofilms are very difficult to kill and have resistances up to one thousand fold more than their planktonic counterparts. Therefore, it is desirable to have a technology which can prevent biofilm growth on implants. Herein we demonstrate that the room temperature silica sol-gel process can be used to form thin films incorporating vancomycin and famesol on metallic implants. We evaluate the characteristics of these thin films and evaluate their bactericidal effects against methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA). We determined that thin sol-gel films release drugs through degradation which is both time-dependent and drug-load-dependent. In addition, it is found that famesol is useful for decreasing the "burst" release ofvancomycin resulting in more controlled drug delivery. It was determined that famesol has bactericidal effects against MSSA, but not against MRSA; however, famesol worked well as an adjuvant to vancomycin. When famesol was used as an adjuvant in combination with vancomycin, a 10 to 1000 fold decrease in bacterial film growth was seen on the implant. These results clearly demonstrated that the novel thin sol-gels films with vancomycin and famesol can be used for targeted drug delivery on implants to substantially prevent bacterial biofilm growth.

碩士
國立中正大學
化學研究所
90
Abstract Antimony tin oxide films (ATO) and indium tin oxide films (ITO) have high electrical conductivity and high optical transparency. By sol-gel process, a metal oxide network of ATO or ITO can be obtained via hydrolysis and polycondensation of the precursor (metal alkoxide or metal salt). Such reactions are characterized as nucleophilic substitutions and can be modified by the choice of the precursor, solvent and additives; they can also be explained by the partial charge model based on balance of electronegativity. Partial charge model not only can illustrate how charges distribute in a molecule but can also predict if a reaction will occur. Metal alkoxides have high reactivity and are easily hydrolysed. The nature of the alkoxyl group influences not only the hydrolysis and polycondensation reactions but also the property of the film. Using metal alkoxide〔M(OR)n〕 as the precursor, the hydrolysis ratio h (H2O/M) must go between 1 and n (1＜h＜n) to produce fine gels. Metal salts can also undergo hydrolysis and polycondensation reactions that are strongly dependent on pH. The higher the pH the larger will be the hydrolysis ratio. If highly polycondensed products are desired, the reactions should be carried out at a pH close to the zero charge point of the metal oxide. In order to control and improve the sol-gel process, additives are used to obtain films of higher qualities. Adding PVA (poly-vinyl alcohol) into the sol can efficiently prevent the gel from cracking. Also, additives such as AcOH (acetic acid), acaH (acetyl acetone), can be used to form stable compounds and lower the function of the precursor to facilitate the formation of gel as well as monodispersed particles. The electrical conductivity of these films arises from the high concentration of carriers and oxygen deficiency. As such, moderate doping can efficiently increase the concentration of carriers, and the best proportion of Sb in ATO would be 6at% ~ 10at%, while that of Sn in ITO would be 4at% ~ 8at% or 8wt% ~ 15wt%. Controlling the atmosphere (vacuum, argon, nitrogen, nitrogen/hydrogen) during the process of heat-treatment increases oxygen deficiency. Meanwhile, higher oxygen deficiency also exists near surface of the films. Coating method can also influence the property of the film. Films produced by spin coating not only has smaller electrical resistivity, but also a smooth face as well as fine optical quality. Coated films that go through proper drying and then undergo heat-treatment have a lower possibility of cracking than those that undergo heat-treatment directly without drying first. Furthermore, it is better to dry for 30 minutes at a temperature of 150℃. However, cracks are produced easily if the calefaction speed is too fast. Therefore, it is better to maintain the calefaction speed between 20℃/min and 2.5℃/min, with the temperature between 500℃ and 600℃, and with the calefaction time between 30 and 60 minutes. If laser or infrared ray is used to accelerate heat-treatment, the electrical resistivity of the films is lowered by 2 to 5 times than that by heat-treatment with electric stove. The electrical resistivity of ATO produced by the sol-gel process is still a little high, but the electrical resistivity of ITO produced by the sol-gel process is comparable with other methods. Furthermore, ITO films prepared by the sol-gel-derived target has a film resistivity one third lower than that by the normal target.

碩士
國立高雄大學
應用物理學系碩士班
100
The optical and structural properties of zinc oxide (ZnO) semiconductor thin film, grown by sol-gel spin-coating technique, were studied by photoluminescence and X-ray diffraction method. First, we examined the effect of 6 growth-conditions on ZnO thin films; (1) Pre-annealing temperature, (2) Post-annealing temperature, (3) aging-time, (4) Molar concentration of Zn2+, (5) Molar ratio of Zn 2+ ：MEA、(6) Film thickness. After acquiring the growth-parameters to obtain ZnO thin film with best optical and structural quality, we further studied the excitonic properties of the ZnO thin film thoroughly. We found that the photoluminescence peak energy of ZnO thin films at room temperature depends on the optical quality of the thin films. Furthermore, the appearance of inelastic exciton-exciton scattering in ZnO thin films depends crucially on the grain-size of the thin films.

碩士
輔仁大學
化學系
101
The research focuses on imprinted sol-gel films as sensing material for recognition of odorants. Seven imprinted sol-gel films in different composition and ratio were fabricated through the molecular imprinting technique. Selectivity of these imprinted sol-gel films was observed toward five different acid odorant. The imprinted sol-gel films were prepared via hydrolysis and condensation of silane monomer in acidic condition. TEOS (tetraethoxylsilane) were used as the main component of silane mixture. MTMOS (methyl trimethoxysilane), APTES (3-aminopropyl-triethoxysilane) and other silane monomer were incorporated into the sol to introduce special functional groups. In this research, acetic acid, propionic acid, butyric acid, valeric acid, and caproic acid were employed as template acid odorant. The specific conformational cavity was created by extracting the template acid odorant after sol-gel process. In the method, the imprinted sol-gel films were coating on the gold electrode of piezoelectric quartz crystal which was modified with thioglycolic acid. The piezoelectric sensor was used to investigate the binding affinity of the imprinted sol-gel films with the target acid odorant. Selective adsorption of the imprinted sol-gel films were measured by mass change with frequency analysis. The sensitivity and selectivity of imprinted and non-imprinted sol-gel films toward five different acid odorant were also studied.

碩士
國立交通大學
材料科學與工程研究所
85
In this work we studied the preparation, structure and properties of Ta2O5 films grown by sol-gel method. The specimems were prepared byspin-coating the starting solution containing Ta(OC2H5)5 onto Si wafersfollowed by various heat treatments. X-ray and AES analyese indicted atthe film has [O]/ [Ta] ratio rather close to exact stoichiometry. The films annealed at 400℃for 4hrs exhibited the highest dielectric constant (24.27) and the best breakdown voltage (1.23MV/cm). However, as revealed by TEM, SEM and AFM characterizations, the Ta2O5 films prepared by sol-gelmethod contained many micro- defects and voids which severely restricted their electrical performance. Recrystallization during further annealsinduced even more defects in Ta2O5 films, which showed no benefication of both structure and electrical properties of the films.

碩士
遠東科技大學
機械工程研究所
100
This study is related to the synthesis and characteristics of SiOC film prepared by sol-gel method in combination with the spin coating method (SOD). The purpose of adding a specific chemical agent is used as a carbon source to introduce carbon to SiO2 film and to form porous materials. The pre-solutions were adjusted pH with acetic acid or ammonium hydroxide. According to the expetimental results, the precursor at pH 3 was chosen to deposit the films, which were spin-coated on cleaned glass or silicon substrates. After spin-coating, the films were baked at 150 oC for 5 min. Finally, the coatings were annealed in a horizontal quartz-tube furnace at 300o and 550o for 30 minutes. The morphology of porous materials was observed with scanning electron microscopy (SEM), and the pore size was measured by BET (Brunauer–Emmett–Teller). The binding state of the films was performed with Fourier transform infrared spectrometer (FTIR). The optical transmittance of the SiOC films deposited on glass substrate was measured at normal incidence with UV/Visible Spectrophotometer. The correlation of characteristics between the pH and aging time on hydrolysis and condensation reaction of TEOS based pre-solution was explored. At the same time, characteristics of the SiOC films were also discussed.

碩士
國立高雄應用科技大學
化學工程與材料工程系博碩士班
105
In this study, the ZnCo2O4 thin films were prepared on quartz and glass substrate by sol-gel method. The sol-gel derived thin films were annealed at 300~400℃ in O2 for 2 hours. Single ZnCo2O4 phase exists at 300~400℃ with both substrates. For the quartz substrate , the optical bandgap of thin films is 2.47~2.50 eV with the maximum transmittance of 80% . For the glass substrate, the optical bandgap of thin films is 2.41~2.42 eV with the maximum transmittance of 55%. The thickness of the ZnCo2O4 thin films was about 120 nm. Three Raman vibration modes including Eg, F2g and A1g were found in the ZnCo2O4 thin films. The best electrical resistivity of the ZnCo2O4 thin films was found at the annealed specimen at 3500C.The electrical conductivity of the ZnCo2O4 thin films was 19.71±0.26 Ωcm. Using the same method to prepared the Mg-doped ZnCo2O4 thin films on the glass substrate is also provided. The optical bandgap of thin films is 2.31~2.47 eV with the maximum transmittance of 55% . The electrical resistivity of the Mg-doped ZnCo2O4 thin films was reduced to 82.85% compare to the thin films without Mg-dopant. The best electrical properties of the thin films occurs at 5%-Mg doping was 3.38±1.42 Ωcm. Keywords: sol-gel method, ZnCo2O4 , thin films, Mg-doped

碩士
國立中央大學
材料科學與工程研究所
97
In this study, the superhydrophobic epoxy-based thin film was prepared by mixing epoxy polymer solution and MTMOS solution first, and then the silica powder and PET fibers were added into the mixing solution to increase the roughness and improve the adhesion of the hybrid film, respectively. The characteristic of the film was analyzed by contact angles, adhesion test, SEM images, and AFM results. The experimental result indicated that when the mole fraction of MTMOS increased from 0 to 0.4, the contact angle of the film also increased from 77° to 98°. And no matter the mole fraction of MTMOS was 0 or even 0.4, the remaining area of the films after the adhesion test were all 100%. To increase the surface roughness of the film, the coating solution was prepared by mixing the solution with silica powder. When the ratio of silica powder was 30wt%, the contact angle could be increased from 98° to 149°, but remaining area of the film decreased to 85% in the contrary. Furthermore, to improve the adhesion between the film and substrate, the coating solution was prepared by mixing the above solution with PET fibers. The remaining area after the adhesion test could be promoted to 95% as long as the addition of PET fibers was only 0.05wt%. In addition, the contact angle was also increased to 153° because of the increase of the roughness. In the other hand, the remaining area after the adhesion test could be increased to 100% while the curing temperature was increased to the range of 130˚C and 180˚C. Moreover, the corrosion test result showed that the corrosion area on the aluminum substrate was reduced obviously after coating the superhydrophobic film on it.

碩士
國立成功大學
材料科學及工程學系碩博士班
96
In recent years, electrochromism has been extensively utilized due to its potential application in smart windows utilized in architecture and those in automobile glazing. These have its repercussions in preventing energy wastage concomitant with modulation of light and solar radiation transmission.In this study, the precursor solutions were synthesized by sol-gel method while conventional low cost spin –coating technique was utilized for deposition of thin films, no need of high vacuum. Experimental results indicated that the WO3 films comprising of 2M H2O2 concentration exhibited the optimum electrochromic properties. WO3 films were found to retain their amorphous phase up to 300oC. The onset of the crystalline phase occurs at 400oC and it become completely crystalline at 500oC. After annealing the electrochromic properties of WO3 deteriorate, however their chemical stability is better than the amorphous counterparts. At the last, the polystyrene intermediate layer was used in order to generate porosity in the WO3 layers, eventually enhancing their surface area. This leads to improve its electrochromic properties and retent its chemical stability, which is the prime requisite for applications in smart windows.

碩士
國立中山大學
電機工程研究所
85
The La-modified lead titanate (PLT) thin films were deposited on Pt/SiO2/Si substrates by spin coating with sol-gel processing in this thesis. 1,3 Propanediol was used as solvent to minimize the number of cycles of spin coating and drying processes to obtain the desired thickness of thin film. By changing the La content (0~20 mole%) and the heating temperature (500~800℃), the effects of various processing parameters on the thin films growth are studied. The results will be adopted as the basis to develop the devices of infrared Sensors in the future. Experimental results reveal that the La contents will influence strongly on the grain size, dielectricity, ferroelectricity and pyroelectricity of PLT thin films. With the increase of La content, the relative dielectric constant of PLT thin films increases from 53 up to 101 with a maximum value of εr existing at the heating temperature of 700℃. We also found that tanδ decreased from 0.00274 to 0.00062, EC decreased from 17.1 KV/cm to 5.9 KV/cm, and Pr decreased from 1.72μC/cm2 to 1.3μC/cm2 but γ increased from 2.6x10-8 C/cm2K up to 3.15x10-8 C/cm2K with the increase of La content. Besides, the results of experiment also show that the PLT thin film possesses a lower current density and a larger pyroelectric coefficient at the heating temperature of 700℃ and La content of 20 mole %.

碩士
中原大學
物理研究所
100
In this study, we used the sol-gel method to prepare ZnO films and Al doped ZnO films. We investigated how the speed of spin coating, annealing temperature and annealing atmosphere affect the ZnO films, and how the Al doping affects the AZO films. In our experiments, we used scanning electron microscope (SEM) to analyze surface morphology, energy dispersive X-ray spectrometer (EDS) to measure sample composition, X-ray diffraction (XRD) to analyze crystal phase, photoluminescence (PL) to measure band gap, the van der Pauw method to measure resistivity, and UV/VIS spectrometer to measure transmittance of the ZnO and AZO films. Then we used these results to explain our experimental data. The resistivity of pure ZnO films prepared on glass substrates is about 30 Ω-cm. It reduces to about 0.02 Ω-cm after Al doping, and the transmittance of the films is higher than 80% in visible region. To decrease the resistivity, we annealed the sample in Ar to increase the vacancies of oxygen. Then we found that the resistivity of pure ZnO films decreases to ~8 Ω-cm and the resistivity of AZO films decreases to ~3×10-3 Ω-cm. The transmittance is still kept higher than 80%.