Orientador: Steven Frederick Durrant / Banca: José Humberto da Silva / Banca: Douglas S. Galvão / O Programa de Pós Graduação em Ciência e Tecnologia de Materiais, PosMat, tem caráter institucional e integra as atividades de pesquisa em materiais de diversos campi / Resumo: Filmes finos de carbono amorfo hidrogenado contendo silício e dopados com flúor foram produzudos pelos métodos de Deposição de Vapor Químico Assistido e Plasma (PECVD) e Deposição e Implantação Iônica por Imersão em Plasma (PIIID). Para PECVD foi utilizada uma pressão total de gases/vapor de 100 mTorr e inicialmente, 100W de potência de excitação. A proporção dos gases foi estudada, mantendo a concentração do hexametildisiloxano (HMDSO) em 75% e variando a proporção do argônio (Ar) e do hexafluoreto de enxofre (SF6). As porcentagens de flúor utilizadas na alimentação do plasma variaram em 0,6,9 e 12,5%. Visando maior concentração atômica de flúor na estrutura dos filmes, determinou-se a proporção de gases/vapor mais apropriada (75% HMDSO, 19% Ar e 6% SF6), e posteriormente, foi realizado um novo estudo da potência de excitação. Variando a potência entre 40 e 70 W, 50 W foi considerada como sendo a melhor condição de excitação para a descarga luminosa, considerando os efeitos causados pela corrosão relacionada ao flúor e a incorporação do elemento. Um estudo sobre as mesmas proporções foi realizada pela técnica de PIIID, com uma pressão total de 50 mTorr, potência de 50 W e pulsos negativos com magnitude de 800 V. Para este método o filme produzido com 12,5% de SF6 foi escolhido como sendo a melhor opção, tendo em vista que apresentou a maior quantidade atômica de flúor em sua estrutura. Posteriormente, a intensidade dos pulsos aplicados foi variada entre 544 e 14801 V, onde verificou-se que o aumento da intensidade dos pulsos resulta na diminuição da incorporação de flúor / Abstract: Hydrogenated amorphous carbon films containing silicon and doped with fluorine were produced by two methods: Plasma Enhanced Chemical Vapor Deposition (PECVD) and Deposition (PIIID). For PECVD a total pressure of 100 mTorr was used at a excitation power of 100 W. The gas/vapor proportion was studied, keeping 75% hexamethyldisiloxane and varying the argon (Ar) and sulfur hexafluoride (SF6) ratio. The following proportions of SF6) ratio. The following proportions of SF6 were examined: 0, 6, 9 and 12.5%. Aiming for the highest atomic concentration of fluorine in film structure the best condition (75% HMDSO, 19% Ar and 6% SF6) was determined and a new study of the influence of the radiofrequency power. Considering the corrosion effects gernerated by fluorine in the plasma, variation of the applied power between 40 and 70 W, allowed the selection of 50 W as the best conditions. A study employing the same proportior PIIID was performed using 50 mTorr of total pressure, an applied power of 50 W and a pulse bias of 800 V. Considering the results of the chemical characterizations, films were produced with 12.5% of SF6 in the plasma feed. Subsequently, bias voltage was varied between 544 and 1480 V, where it was observed that the increasing the pulse bias decreased the fluorine concentration in film structure / Mestre

Amorphous a-SiNx (:H) films have been prepared by radio-frequency sputtering in an argon-nitrogen-hydrogen atmosphere. Both hydrogenated and non-hydrogenated films were studied along with films prepared by the glow-discharge decomposition of a gaseous mixture of silane and ammonia. Photoemission experiments were performed on the sputtered samples. The position and strength of the core levels were determined, along with the plasma energies as a function of x. A comprehensive study of the number and types of defects present within a-SiN(:H) was undertaken. Films sputtered at room temperature and at 200°C, both with and without hydrogen, were studied along with films prepared by the glow-discharge technique. The results obtained are discussed in the light of existing models. Certain characteristic energies obtainable from optical data have been found for hydrogenated and non-hydrogenated films. These results are then related to other experimental results, in particular those from photoemission measurements. Reflection measurements have been made in the range 0.5eV to 12eV on the sputtered and glow-discharge films. From the reflection measurements e2 spectra were determined by Kramers-Kronig analysis. The dependence of the optical joint density of states with alloying was found from the data. It was found from these measurements that the top of the valence band gradually changes from Si3p states to N 2p states.

The use of aluminium alloy films, and in particular Al-1%-Si, is common in many microelectronic interconnection schemes. Specular reflectivity and sheet resistance measurements are often used to characterise the deposited film. These and other properties, such as electromigration resistance, are dependent on the film's structure. An understanding of the relationship between the film structure and its properties is therefore important. Al-1%-Si films were deposited using dc magnetron sputtering onto (100) silicon substrates with or without thermal or deposited oxide layers. The film grain size and orientation were determined using scanning electron microscopy and X-ray diffraction measurements respectively. The orientation was quantified by the ratio of the X-ray diffraction intensities from the (111) and (200) planes. The structure of Al-1%-Si films depended strongly on film thickness using continuous mode deposition, and on substrate position using batch mode. For both modes of deposition the X-ray diffraction ratio was dependent on the substrate used. By careful choice of monitor substrate, and control of deposition conditions, the film structure could be successfully predicted and controlled. The specular reflectivity of Al-1%-Si films has been shown to depend on their roughness, optical properties and grain size, and the measurement wavelength. Of particular importance in determining the specular reflectivity is the substrate used as well as its position for batch mode deposition. The critical dimension size and automatic alignment accuracy obtained during the photolithographic patterning of the deposited film depended on its specular reflectivity. This shows that specular reflectivity control, especially for a batch deposition process, is important. Finally, room temperature sheet resistance has been shown to vary with the substrate used and substrate position during batch mode deposition.

No description available.

In this study, two kinds of mesoporous materials were prepared. The first was a silica mesostructure grown within a porous aluminium oxide membrane columnar material (hybrid-AOM). This was prepared using a sol-gel technique with Pluronic P123 triblock copolymer as the structure-directing agent and tetraethyl orthosilicate as the inorganic source. The hybrid-AOM had a similar pore size distribution to that of as-prepared SBA-15 but showed an amorphous character, as demonstrated by nitrogen adsorption and SAXRD. The second type of material was a continuous mesoporous silica thin film, prepared by the dip-coating technique using Pluronic F127 triblock copolymer as the structure-directing agent and the same silica source as hybrid-AOM. The film, which was self-assembled on substrates such as indium tin oxide (ITO), glass and gold, exhibited long-range ordered mesostructures after several treatments and aging. Grazing incidence small-angle X-ray scattering method (GISAXS) showed that the thin film contracted in a direction perpendicular to the substrate after drying and surfactant removal.Removal of the surfactant template from both materials in order to create porous silica was achieved by calcination, ethanol extraction and peroxide-Fe treatments. Calcination was found to be the best method to remove surfactant from both mesostructures (hybrid-AOM and thin film). However, this was found to cause cracking and crumpling of the hybrid-AOM with the evaporated gold being easily peeled off after calcination. Ethanol extraction was thus applied where calcination was not suitable. The surfactant removal was confirmed using an infrared spectroscopy and the structure was confirmed after extraction using 1D X-ray diffraction (XRD). The surface morphology, porosity and crystallinity of the mesostructures prepared were characterized by nitrogen adsorption, scanning electron microscopy and small angle XRD. To form modified electrodes, the hybrid-AOM template was coated by evaporation with pure gold on one side, whilst the mesostructured thin film was grown on either gold or ITO. The permeability of the void space for both hybrid and thin film samples was calculated from the cyclic voltammetry response of a neutral probe (FcMeOH). Cationic ([Ru(bpy)3]2+) and anionic (I-) electroactive species were used to observe the electrochemical response under different pH regimes. FcMeOH was also used to study the effect of KCl concentration on the silica surface charge. Gold and platinum were electrochemically deposited using mesoporous silica as a template.

Carbon encapsulated metal nanoparticles are an increasingly important class of materials due to the wide range of electronic, magnetic and mechanical properties they display. However, traditional deposition techniques are often complex or lead to a poor quality film. Ionised magnetron sputter deposition is a promising development to traditional magnetron sputtering which combines film deposition with ion bombardment. By adding an RF powered, inductively coupled plasma positioned between the deposition targets and the substrate, the ionisation fraction of the depositing flux is greatly increased. This additional ion flux can then be controlled through the use of an electrical substrate biasing. This controls the energy flux to the surface and therefore the resulting microstructure. Carbon-nickel thin films were grown by ionised magnetron sputter deposition. The films themselves were characterised using a wide variety of techniques to measure not only their structure but their properties. Additionally, the inductively coupled plasma itself was characterised using a Langmuir probe. It was determined that upon application of a negative substrate biasing, the ion flux to the growing film remained constant, however the energy of the species increased. This resulted in a columnar structure of nickel carbide which coarsened as the bias (and therefore the energy of the ions) was increased. Conversely the application of a positive bias gives a large flux of low energy bombardment. This led to the formation of metallic nickel nanoparticles (? 30 nm diameter) which were surrounded by several layers of ordered graphitic shells forming a so-called "nano-onion" structure. The transition between these phases is a result of an increase in adatom mobility when there is a high flux, low energy ion bombardment which allows the nickel and carbon to phase separate. Upon separating, the nickel templates graphite growth due to their similar bond lengths leading to the formation of the graphitic cages. The transition between these two structures is measured through X-ray diffraction which shows a transition from the hexagonal carbide phase to the cubic nickel phase. This is accompanied by an increase in ordering of the carbon as the bias is increased as measured by Raman spectroscopy. Additionally, it is observed that there is an increase in carbon ordering when a negative bias is applied, due to the additional energy from ion bombardment leading to graphite formation. Magnetic measurements showed a transition from a non-magnetic state when the structures were largely carbide, to a magnetic state when metallic. However at room temperature the structures display superparamagnetic behaviour due to the small size of the particles. Measurements of electronic conductivity showed a negative temperature coeffcient of resistivity for all samples demonstrating no metallic conduction path was present. A large drop in resistivity as the temperature increases was assigned to thermally activated conduction. At low temperatures the conductivity is dependent on tunnelling across small regions of amorphous carbon, while at higher temperatures it is possible to excite the electrons into a conduction band allowing them to conduct more easily.

A study of the structural and electrical properties of low-temperature-sublimed silicon films indicates that they are characterized by a high density of grain boundaries, hence crystal defects. A trapping model has been proposed to explain the experimentally observed temperature-dependencies of resistivity and carrier concentration of these films. The result shows that the defect density at the grain boundaries is of the order of 10¹² cmˉ², and that it is independent of the doping concentrations in the films. It has been shown that the thin-film metal-insulator-semi-conductor (MIS) structure can be reduced to a transmission line problem by expressing the equivalent capacitance of the structure as a series combination of the depletion capacitance and the insulator capacitance. The variations of both the capacitance and channel conductance of the MIS structure have been utilized to make notch filters in which the notch frequency can be varied over 200% by an external biasing voltage. In view of the need for maintaining a constant null depth in the semiconductor notch filter under various biasing potentials, a new notch network has been proposed in which the optimal notch condition could be maintained simply by designing the ratios of the lengths and widths of the MIS structure to the appropriate values. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

A study has been made of the properties of thin yttrium oxide dielectric films prepared by the electron beam evaporation of high purity Y₂O₃ powder. Films deposited on freshly cleaved NaCl crystals and on polished n-type silicon were examined in the electron microscope. The specimens were found to be polycrystalline, with a crystal size of the order of 100 Å. The structure was found to be essentially the same as found for bulk Y₂O₃. D.C. conduction measurements were made on films of various thicknesses. The characteristics were found to be bulk-limited, with the conductivity decreasing at lower pressures. An activation energy of 0.6 eV was found. The conduction mechanism was believed to be Poole-Frenkel emission of electrons from donor centers into the Y₂O₃ conduction band. The donor centers were believed to be interstitial yttrium atoms rather than oxygen vacancies because of the pressure dependence observed in conductivity. Step response measurements were made, and the results explained on the basis of a loss peak with a most probable relaxation time of 200 seconds. The relaxation of oxygen atoms dissolved in the anion defective Y₂O₃ lattice was assumed to be the mechanism. The results of step response and A.C. bridge loss measurements indicated that different relaxation mechanisms are dominant in different frequency ranges. Internal photoemission measurements were made on Al-Y₂O₃-Al sandwiches. The energy barrier between the electrodes was found to be trapezoidal, with barrier heights of 3.14 and 3.72 eV. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

The work contained in this thesis is concerned mainly with conduction mechanisms and polarization processes in thin amorphous insulating films. A model has been proposed and its d.c. conduction characteristics computed. The numerical results show the possibility of obtaining either space charge, Schottky, or Poole-Frenkel characteristics depending on the model parameters. The transient electronic discharge current has been analysed and the results show that this electronic current is approximately independent of the preapplied voltage in contrast to the ionic discharge current which is linearly dependent on preapplied voltage. This result, together with the experimental results obtained on Ta/Ta₂O₅/Au diodes, suggests that the calculations of low frequency dielectric losses using step response measurements are complicated by space charge effects only when the preapplied field is relatively low (≤lMV/cm for Ta₂0₅ films). Ta/Ta₂O₅/Au diodes were prepared by solution anodization or plasma anodization. All prepared diodes exhibited a rectification behaviour. Over the frequency range 100 Hz -100 kHz capacitance and loss tangent were found to decrease slightly with increasing frequency while the equivalent series resistance was found to be approximately proportional to ω⁻¹‧º⁵. All prepared diodes, with gold counter electrodes less than 1000 Å thick, were found to withstand, under a slowly applied field, field strengths approaching the formation field value. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

This thesis presents the results of a comprehensive research study of the bearing behaviour of single or multiple bolted plates in bolt shear at ambient and elevated temperatures. A total of 18 tests were carried out to provide detailed experimental information on bearing behaviour of plates with single bolt. A series of parametric studies using the commercial finite element package ABAQUS were conducted to investigate the effects of different design parameters on the connected plate bearing behaviour, including initial stiffness, ultimate resistance and deformation at the ultimate resistance. The finite element models were verified by comparing the simulated results against the author’s tests conducted as part of this research and other researchers’ test results. Based on the parametric study results, an analytical model was proposed to predict the bearing load-deformation relationship of bolted plate in bolt shear. It was found that the stiffness and ultimate resistance could be predicted accurately by using existing methods. The main contribution of the analytical study was the development of a simple method to calculate the maximum plate deformation (bolt-hole elongation) at the ultimate resistance, based on proposed strain distributions according to different failure modes. This method has been verified against the parametric study results and has been found to be suitable for ambient and elevated temperature applications.