Thesis. 1978. Ph.D.--Massachusetts Institute of Technology. Dept. of Physics. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Bibliography: leaves 225-239. / Ph.D.

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過去幾十年當中，金屬玻璃（包括塊狀金屬玻璃）中非晶相分離的發生已經成為了一個具有爭議性的課題。一些報告報導在具有負混合熱的Pd-Ni-P合金體系中發生了非晶相分離。然而，有一些報告聲稱相分離不能在Pd-Ni-P非晶合金中被觀察到。文獻分析表明，困難在於缺乏直接的實驗證據。 / 為了解決這個難題，示差掃描量熱儀、高分辨電子顯微鏡、掃描透射模式下的高角環射暗場相、以及能量色散X射線光譜儀等檢測儀器在我們實驗當中被使用。同時為了清楚展示非晶相分離反應，在過冷Pd₄₁.₂₅Ni₄₁.₂₅P₁₇.₅熔體被冷卻為固態非晶樣品之前引入了中間熱退火處理。 / 實驗研究了三種經由不同路徑製備的A、B、C型號樣品。結果表明在非晶/液態Pd₄₁.₂₅Ni₄₁.₂₅P₁₇.₅合金中可能存在獨特的短程有序結構，它會導致相分離的發生。同时研究發現，在大約625 K，調幅分解的持續時間的下限大概是200 s。調幅分解的時間常數R在大約625 K 下為0.002 s⁻¹。三种类型样品在不同的溫度下被退火從而獲得部分的結晶。A型號和B型號具有相似的行為。在低溫下，圓形的核心首先形成，接著發生共晶反應。在高溫下，出現了一種形狀為立方體的析出相。在C型號的樣品當中，核心和立方的析出物同時被發現。但是核心的成分分佈與A和B型號中出現的不同。同時，隨著退火時間的加長形核的數量也具有獨特的行為表現。作為對比，Pd₄₀Ni₄₀P₂₀塊狀金屬玻璃的結晶行為也被展開了研究。同樣的，以形成核心開始，但是它的成分分佈異於A和B型號的樣品。 / Amorphous phase separation in metallic glass (including bulk metallic glass) has been a controversial issue in the past several decades. There are reports saying that amorphous phase separation occurs in Pd-Ni-P, which has a negative heat of mixing among its constituent elements. However, there are also as many reports claiming that phase separation is absent in amorphous Pd-Ni-P alloys. The lack of direct experimental evidence makes the issue to be difficult to be resolved. / To solve this problem, differential scanning calorimetry (DSC), high resolution transmission electron microscopy (HRTEM), high angle annular dark field (HAADF) in scanning transmission electron microscopy, and energy dispersive X-ray spectroscopy (EDX) have been employed. Intermediate thermal annealing is introduced before an undercooled Pd₄₁.₂₅Ni₄₁.₂₅P₁₇.₅ melt is cooled down to become a solid amorphous specimen. / A-type, B-type, and C-type specimens of composition, Pd₄₁.₂₅Ni₄₁.₂₅ P₁₇.₅, have been prepared via three different cooling paths. It was found that amorphous phase separation indeed occurs in C-type specimens. Results suggest that there may be unique short range orders in amorphous/liquid Pd₄₁.₂₅Ni₄₁.₂₅P₁₇.₅, which are responsible for the phase separation. Experimental arrangements were made to study the occurrence of spinodal reaction in undercooled molten Pd₄₁.₇₅Ni₄₁.₇₅P₁₇.₅ alloys as a function of time. The lower bound of the duration of the spinodal decomposition at a temperature of {U+2248}625 K is about 200 s and the time constant R of the spinodal decomposition at a temperature of {U+2248}625 K is 0.002 s⁻¹. / A-type and B-type specimens have similar crystallization behavior. At low temperature, it starts with the formation of a spherical core and then eutectic crystallization takes over. At higher temperatures, an additional phase in the shape of a cube appears. In annealed C-type specimens, cores and cubic precipitates are also found. However, the composition profile of the cores is different and the number of nucleation events versus time has peculiar characteristics. The crystallization behavior of Pd₄₀Ni₄₀P₂₀ BMG was studied for comparison. It again starts out with the formation of a core, but with a composition profile different from those of A-type and B-type specimens. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Lan, Si = 對於具有負混合熱的塊狀金屬玻璃非晶相分離的研究 / 蘭司. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references. / Abstract also in Chinese. / Lan, Si = Dui yu ju you fu hun he re de kuai zhuang jin shu bo li fei jing xiang fen li de yan jiu / Lan Si. / Abstract of thesis --- p.i / Acknowledgements --- p.v / List of Tables --- p.x / List of Figures --- p.xi / Chapter Chapter 1 --- Introduction and literature review --- p.1 / Chapter 1.1 --- Introduction to metallic glasses --- p.1 / Chapter 1.1.1 --- Background of metallic glasses --- p.1 / Chapter 1.1.2 --- Glass transition --- p.2 / Chapter 1.1.3 --- The undercooling of liquids --- p.3 / Chapter 1.1.4 --- Crystal nucleation and growth in liquids --- p.3 / Chapter 1.1.4.1 --- Crystal Nucleation in liquids --- p.3 / Chapter 1.1.4.2 --- Crystal growth in liquids --- p.5 / Chapter 1.1.4.3 --- TTT diagram --- p.6 / Chapter 1.1.4.4 --- Crystallization in metallic glasses --- p.6 / Chapter 1.1.5 --- Glass formation methods and systems --- p.6 / Chapter 1.1.6 --- Glass forming ability and criteria --- p.8 / Chapter 1.1.7 --- Properties and applications --- p.9 / Chapter 1.2 --- The basic theory of phase separation in a binary system --- p.10 / Chapter 1.2.1 --- Thermodynamic background --- p.10 / Chapter 1.2.2 --- Solid state phase separation --- p.11 / Chapter 1.2.2.1 --- A miscibility gap of binary mixture --- p.11 / Chapter 1.2.2.2 --- Nucleation and growth mechanism --- p.12 / Chapter 1.2.2.3 --- Spinodal decomposition mechanism --- p.13 / Chapter 1.2.3 --- Liquid state miscibility gap in a binary system --- p.21 / Chapter 1.3 --- Literature review for phase separation in metallic glasses --- p.23 / Chapter 1.4 --- The aim of this thesis --- p.28 / Figures --- p.30 / References --- p.39 / Chapter Chapter 2 --- Experiments and characterization --- p.44 / Chapter 2.1 --- Introduction and the outline of the experiments --- p.44 / Chapter 2.2 --- Sample preparation --- p.45 / Chapter 2.2.1 --- Bulk metallic glasses preparation --- p.45 / Chapter 2.2.1.1 --- Preparation of clean fused silica tubes --- p.45 / Chapter 2.2.1.2 --- Weighing --- p.46 / Chapter 2.2.1.3 --- Alloying --- p.46 / Chapter 2.2.1.4 --- Fluxing --- p.47 / Chapter 2.2.2 --- Thermal annealing --- p.49 / Chapter 2.2.3 --- Specimens preparation for characterization --- p.50 / Chapter 2.2.3.1 --- Cutting, molding, grinding and polishing --- p.50 / Chapter 2.2.3.2 --- Etching --- p.51 / Chapter 2.2.3.3 --- Thinning for TEM foils --- p.51 / Chapter 2.3 --- Characterization --- p.55 / Chapter 2.3.1 --- Differential scanning calorimetry (DSC) --- p.55 / Chapter 2.3.2 --- Scanning electron microscopy (SEM) --- p.55 / Chapter 2.3.3 --- Transmission electron microscopy (CTEM and HRTEM) --- p.57 / Chapter 2.3.4 --- High angle annular dark field (HAADF) in Scanning transmission electron microscopy (STEM) --- p.58 / Chapter 2.3.5 --- Energy dispersive X-ray spectroscopy (EDX) --- p.59 / Figures --- p.62 / References --- p.69 / Chapter 3 --- p.70 / Chapter 3.1 --- Introduction --- p.70 / Chapter 3.2 --- Materials and Experimental --- p.73 / Chapter 3.3 --- Results --- p.75 / Chapter 3.3.1 --- Thermal behaviors of three types of specimens --- p.75 / Chapter 3.3.2 --- Microstructures of three types of specimens --- p.75 / Chapter 3.3.2.1 --- A-type specimens --- p.75 / Chapter 3.3.2.2 --- B-type specimens --- p.76 / Chapter 3.3.2.3 --- C-type specimens --- p.76 / Chapter 3.4 --- Discussion --- p.78 / Chapter 3.5 --- Conclusions --- p.79 / Chapter 3.6 --- Afterward --- p.79 / Figures --- p.80 / References --- p.89 / Chapter Chapter 4 --- The time constant of the spinodal decomposition in Pd₄₁.₇₅Ni₄₁.₇₅P₁₇.₅ bulk metallic glasses --- p.92 / Chapter 4.1 --- Introduction --- p.92 / Chapter 4.2 --- Materials and experimental --- p.92 / Chapter 4.3 --- Results --- p.94 / Chapter 4.3.1 --- Thermal behaviors --- p.94 / Chapter 4.3.2 --- Microstructures --- p.94 / Chapter 4.4 --- Discussion --- p.96 / Chapter 4.5 --- Conclusions --- p.98 / Figures --- p.100 / References --- p.123 / Chapter Chapter 5 --- Crystallization in homogeneous and phase-separated Pd₄₁.₂₅Ni₄₁.₂₅P₁₇.₅ bulk metallic glasses --- p.125 / Chapter 5.1 --- Introduction --- p.125 / Chapter 5.2 --- Experiments --- p.126 / Chapter 5.3 --- Results --- p.128 / Chapter 5.3.1 --- Low temperature thermal annealing at 613 K with 0≤t{U+2090} ≤ 8 h --- p.128 / Chapter 5.3.1.1 --- A-type and B-type specimens --- p.128 / Chapter 5.3.1.2 --- C-type specimens --- p.130 / Chapter 5.3.1.3 --- Pd₄₀Ni₄₀P₂₀ BMG --- p.132 / Chapter 5.3.2 --- High temperature thermal annealing --- p.133 / Chapter 5.3.2.1 --- A-type and B-type specimens --- p.133 / Chapter 5.3.2.2 --- C-type specimens --- p.135 / Chapter 5.3.2.3 --- Pd₄₀Ni₄₀P₂₀ BMG --- p.137 / Chapter 5.4 --- Discussion --- p.137 / Chapter 5.4.1 --- Formation of spherical cores --- p.138 / Chapter 5.4.1.1 --- A-type and B-type Pd₄₁.₇₅Ni₄₁.₇₅P₁₇.₅ specimens --- p.138 / Chapter 5.4.1.2 --- C-type Pd₄₁.₇₅Ni₄₁.₇₅P₁₇.₅ specimens --- p.139 / Chapter 5.4.1.3 --- Pd₄₀Ni₄₀P₂₀ BMG --- p.140 / Chapter 5.4.2 --- Formation of cubic precipitates --- p.141 / Tables --- p.142 / Figures --- p.144 / References --- p.188 / Chapter Chapter 6 --- Conclusions --- p.190 / Bibliography --- p.192

Thesis. 1978. Ph.D.--Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / Ph.D.

Orientador: Elidiane Cipriano Rangel / Banca: José Daniel Biasoli de Mello / Banca: Lúcia Vieira Santos / Banca: Roberto Martins de Souza / Banca: Steven Frederick Durrant / O programa de Pós graduação em Ciência e Tecnologia de Materiais, PosMat, tem carater institucional e integra as atividades de pesquisa em materiais de diversos campi da UNESP / Resumo: Neste trabalho foi investigado o efeito protetivo produzido pela deposição de um filme de Carbono Amorfo Hidrogenado (a-C;H) sobre a a superfície de uma ferramenta de conformação coberta com Nitreto de Titânio (TiN). A força necessária para conformar o material é relativamente alta, em torno de algumas toneladas. Os Filme de a-C;H foram aplicados com o objetivo de reduzir o atrito entre as superfícies da ferramentas de conformação e do material a ser conformado, podendo também gerar um ganho pela redução ou eliminação da lubrificação aplicada na fita na forma de fosfato de zinco ou de óleo de repuxo. As amostras foram construídas a partir do aço Ferramenta AISI M2, através dos processos de usinagem mole, tratamento térmico, retifica a lapidação com subseqûente aplicação da camada de TiN através do processo PVD (Physical Vapor Deposition). Também foi utilizado como subtrato discos de aço AISI M2 sem a camada TiN. As amostras foram inicialmente limpas em um processo de lavagem po ultra-som e subseqüentemente por uma procedimento a plasma. Os filmes foram depositados utilizando-se plasmas de baixas temperaturas de misturas de hidrocarbonetos e gases nobres. Foi utilizada a técnica híbrida de implantação iônica e deposição por imersão em plasmas (IIDIP), aplicando-se pulsos de alta tensão negativa à amostras para promover a deposição mediante a implantação iônica. Neste caso, o acetileno (C2H2) diluído em argônio foi utilizado como mistura precursora da formação do filme. Foi investigado o efeito da amplitude dos pulsos de polarização e da pressão dos gases do plasma nas propriedades dos filmes. As espectroscopias no infravermelho e Raman foram empregadas para se avaliar a composição química e a microestrutura dos filmes. Verificou-se nos espectros de infravermelho que... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In this study, the protective effect by the application of a Hydrogenated Amorphous Carbon (a-C;H) film on the surface of a forming tool containing a titanium nitrite (TiN) layer was investigated. The required force to forming the material is relatively high, around a few tons. The a-C;H films were applied to reduce the friction coefficient between the surface of the forming tool and the raw material, also generating the possibility of the reduction or olimination of the lubrication applied to the tape surface in the form of zinc phosphate and drawing oil. The samples were produced from AISI M2 steel, using soft machining processes, heat treatment, grinding and polishing with subsequent application of the IiN layer by PVD (Physical Vapor Deposition). To permit comparison, AISI M2 steel without the TiN layer was also used as a substrate. The samples were initially cleaned in ultrasonic baths ans subsequently by plasma ablation. Low temperature plasmas of hydrocarbon and noble gas mixtures were used to deposit the films. The hibrid technique of plasma immersion ion implantation and deposition (PIIID) was used, applying high voltage negative pulses to the samples to promote deposition under ion bombardment. Acetylene (C2H2) diluted in argon was used as the gas mixture for film formation. The effect of the pulse magnitude and plasma pressure on the properties of the films, were studied. Infrared and Raman spectroscopies were employed to evaluate the film chemical composition and microstructure. Via the infrared spectra was observed a decrease in the C-H and O-H band intensities with increasing pulse magnitude, but a rise in the gas pressure caused the intensity of C-H bands to increase. Raman spectra of all the films exhibited strong photoluminescence, indicating a significant hydrogen content. The receptivity on the films to water... (Complete abstract click electronic access below) / Mestre

O presente trabalho pretende investigar como é feita a utilização da teoria psicanalítica no cenário da reflexão estética e da crítica de arte contemporâneas. Para tanto, o recorte se concentra em dois pensadores que se tornaram significativos na atualidade, embora não sejam os únicos: o crítico Hal Foster e o historiador da arte Georges Didi-Huberman. O objetivo da investigação é mostrar em que medida os conceitos gerados na práxis psicanalítica possibilitaram interpretações de ruptura no campo da estética tradicional. Essa modalidade de análise só se torna possível uma vez que se abandona o paradigma da psicanálise aplicada, ainda corrente no cenário extraclínico. Por fim, a proposta visa sustentar que a operação do amorfo, gerada no interior da pesquisa, pode lançar luz a certas experiências estéticas que vão da modernidade à pós-modernidade das artes / This work intends to investigate the use of psychoanalytic theory within the aesthetic and critical contemporary art field. To this purpose, this study focuses on two philosophers who have become significant in our time: the critic Hal Foster and the art historian Georges Didi-Huberman. This study aims to show how far the concepts generated in psychoanalytic praxis allowed interpretations that disrupt the field of the traditional aesthetics. This type of analysis is possible once we abandon the paradigm of applied psychoanalysis, which is still current in non-clinical setting. Finally, the proposal wants to argue that the category of the amorphous, generated in this research, may clarify certain aesthetic experiences that range from the modernity of art through the post-modernity

Metallic glass matrix composites have enormous potential stemming from the interplay between crystalline and amorphous phases. This work models such a composite using shear transformation zone dynamics (a modified kinetic Monte Carlo method) for the amorphous phase, and a local Taylor dislocation model for the crystalline phase. An N-factorial experiment using the model is presented examining the effects of crystalline volume fraction, microstructure length scale, and yield stress of the crystalline phase. Each replicate is analyzed for maximum stress, maximum strain, strain energy dissipation, strain localization, and strain partitioning between phases. Regression analysis is used to identify statistically-significant trends in the data. The experiment shows that strain delocalization and the consequent ductility are facilitated by a crystalline phase with a substantially lower yield stress than that of the amorphous matrix. It also shows that increasing crystalline volume fraction alone is insufficient to promote strain delocalization in the case of a crystalline phase with high relative yield stress, and that a lower yield stress for the crystalline phase implies lower maximum stresses supported by the composite. Therefore designers must balance the need for ductility and delocalization against the composite yield stress by finding an optimal combination of volume fraction and crystalline mechanical properties. This work provides continuous functional forms for the relationships between these properties to aid in that optimization process.

Polymorphism and crystallinity are now recognised as important issues in drug development. This is shown by the increased amount of research in this area over recent years. In pharmaceutical development milling is an important unit operation for size reduction to improve powder handling, processing and dissolution rate. The aim of this thesis was to investigate the effect of ball milling (and cryo-milling) on the solid state properties, including amorphous drug formation, of pharmaceutical solids. Milling was carried out using an oscillatory ball mill (Mixer Mill MM301, Retsch GmbH & Co., Germany). In cryo-milling the milling jars were immersed in liquid nitrogen for three min before milling. XRPD was used as the main technique to evaluate the milled samples. Ranitidine hydrochloride (RAN) and indomethacin (INDO) were the model drugs used in this study. It was found that upon milling, RAN form 1 converts to RAN form 2 via an amorphous phase. A faster amorphization rate was observed when the crystalline samples were cryo-milled. Amorphous ranitidine hydrochloride was characterized to have a glass transition (T[g]) range of 13 to 30 �C and a crystallization exotherm (T[c]) between 30 and 65 �C. Conversion was found to occur faster when the temperature of the solid powder was greater than the T[c]. Under various storage conditions, similarly, crystallization of the amorphous phase mainly led to RAN form 2. However, some form 1 and amorphous phase was also detected on the XRPD diffractograms. Using partial least squares regression, the amount of solid form components in the ternary RAN mixtures were successfully quantified. RAN form 2 did not convert to form 1 under any milling (including cryo-milling) or storage conditions used in this study. Overall, RAN form 2 was found to be the thermodynamically stable form and the two (RAN) polymorphs are likely to be a monotropic pair. In a co-milling study of INDO and RAN, the two crystalline drugs were successfully converted into a single amorphous phase after 60 min of co-milling in a cold room (4 �C). The T[g] range (26-44 �C) was also characterized for these mixtures. DRIFTS spectra of the co-milled amorphous samples indicated an interaction had occurred between the carboxylic acid carbonyl (HO-C=O) and benzonyl amide (NC=O) of the INDO molecule with the aci-nitro (C=NO₂) of RAN. Depending on the ratio of INDO to RAN, in general, the amorphous mixtures were stable at 4 �C after 30 days of storage. Crystallization was faster when the binary mixtures were stored at higher temperature or contained higher amounts of RAN in the mixture. Although XRPD and DRIFTS suggested an interaction between the two drugs, co-crystal formation was not observed between INDO and RAN. Ball milling can be used to produce amorphous drug. The rate and extent of amorphization is dependent on the milling conditions. A faster rate of amorphization was observed when the crystalline drugs were cryo-milled. Amorphous drug formation can be made either alone or in combination with another crystalline drug. Amorphization could offer a significant improvement on the dissolution profile and the bioavailability of the poorly water soluble drug - indomethacin. Furthermore, ball milling can also be used to produce a homogenous mix between solids. The �goodmix� effect can be used for seed-induced crystallization or, when the XRPD or Raman data were combined with partial least squares regression, to create a reliable calibration model for quantitative analysis.

Hydrated amorphous silicon dioxide (Si02.nH-,O), or opal-A, is deposited naturally from seepage and runoff water as white or brown rock surface coatings, called 'skins', that often partly obscure rock paintings and engravings, but occasionally, a thin translucent silica skin can form a protective film over rock art. White lustrous silica skins, less than 1 mm thick, occur where seepage water regularly flows from bedding and joint planes, whereas much thinner brown skins form on the sides of boulders and cliffs where runoff water periodically flows. To find the degree of silica skin variability and to determine how climate and rock type affect the properties of silica skins I collected samples at seven Australian and two Canadian rock painting sites that were located in temperate, tropical and sub-arctic regions. The skins had developed on sandstone, quartzite, schist, gneiss and migmatite. I studied the effects of the skins on rock art stability, documented their compositions, textures and structures to establish their common properties, and searched for a way to date the silica which would provide an indication of the minimum age of the underlying art. 1 also made replication experiments to determine factors that influence the properties of artificial silica skins and the rates of their precipitation so that I could propose a mechanism for natural silica skin formation, and ascertain whether an artificial silica skin could act as a protective rock art conservation measure. I was able to subdivide the analysed samples into silica skin Types I, II and III on the basis of their colour (translucent, white or brown), composition (SiO2, Al2O3 and absorbed water contents) and texture (smooth vitreous or vermiform). I propose that silica skins initially begin to form on stable rock surfaces by a process involving a combination of evaporation- and ionic-induced polymerisation of silicic acid in seepage and runoff water. Condensation reactions, random clustering of small silica spheres and deposition of the resulting aggregates eventually produce a thin surficial silica film. Deposition of silica often traps micro-organisms that live in the damp seepage and runoff water zones, and these fossils in finely laminated skins enable the radiocarbon dating of silica deposition, and therefore the dating of rock paintings enclosed by silica. Micro-excavation of silica layers associated with rock art combined with accelerator mass spectrometry gave preliminary radiocarbon determinations that were either consistent with, or contradicted, prevailing opinions about the antiquity of the rock art at selected sites. Experiments using a laser technique for combusting fossilised microorganisms in finely laminated skins were unable to generate sufficient carbon for dating. Catalysis of a mixture of equal proportions of methyl-trimethoxy silane and water produces a translucent stable film that may be suitable as a consolidant, whereas other artificial silica skins made from silica glass and tetra-ethoxy silane develop microfractures on drying, and these are unsuitable as rock art consolidants.

There is an every increasing need to develop more durable and higher performing coatings for use in a range of products including tools, devices and bio-implants. Nano-structured coatings either in the form of a nanocomposite or a multilayer is of considerable interest since they often exhibit outstanding properties. The objective of this thesis was to use advanced plasma synthesis methods to produce novel nano-structured coatings with enhanced properties. Coatings consisting of combinations of aluminum (Al), aluminum nitride (AlN) and amorphous carbon (a-C) were investigated. Cathodic vacuum arc deposition and unbalanced magnetron sputtering were used to prepare the coatings. By varying the deposition conditions such as substrate bias and temperature, coatings with a variety of microstructures were formed. A comprehensive range of analytical methods have been employed to investigate the stoichiometry and microstructure of the coatings. These include Transmission Electron Microscopy (TEM), Scanning Transmission Electron Microscopy (STEM), Electron Energy Loss Spectroscopy, Auger Electron Spectroscopy, X-ray diffraction and Raman spectroscopy. In addition to the investigation of microstructure, the physical properties of the coatings were measured. Residual stress has been recognized as an important property in the study of thin film coatings since it can greatly affect the quality of the coatings. For this reason, residual stress has been extensively studied here. Hardness measurements were performed using a nano indentation system, which is sensitive to the mechanical properties of thin films. This thesis undertook the most comprehensive investigation of the Al/AlN multilayer system. A major finding was the identification of the conditions under which layers or nanocomposite form in this system. A model was developed based on energetics and diffusion limited aggregation that is consistent with the experimental data. Multilayers of a-C and Al were also found to form nanocomposites. No hardness enhancement as a function of layer thickness or feature size was observed in either the Al/AlN or a-C/a-C systems. It was found that the most important factor which determines hardness is the intrinsic stress, with films of high compressive stress exhibiting the highest hardness. Nano-structured multilayers of alternating high and low density a-C were investigated. For a-C multilayers prepared using two levels of DC bias, evidence of ion beam induced damage was observed at the interfaces of both the low and high density layers. In addition, the structure of the high density (ta-C, known as tetrahedral amorphous carbon) layers was found to be largely unchanged by annealing. These results extend our understanding of how a-C form from energetic ion beams and confirms the thermal stability of ta-C in a multilayer. This thesis also presented the first attempt to synthesis a-C multilayered films with a continuously varying DC bias in sinusoidal pattern. The resulting films were shown to have a structurally graded interface between layers and verified that ion energy and stress are the most important factors which determine the structure of a-C films.