The bottom-up processing techniques used for making Microelectromechanical systems (MEMS) devices can produce material properties different from bulk processing. The material properties must be evaluated with the process parameters used and for changes in the process parameters. The mechanical properties are needed to design MEMS devices. A material of interest for MEMS devices is nickel titanium (NiTi) shape memory alloy (SMA) because of the high work output (~107 J/m3). This thesis will focus on the fabrication of thin film NiTi by DC magnetron sputtering deposition and testing mechanical properties of the fabricated films by nanoindentation. Thin film NiTi SMA was successfully created by DC magnetron sputtering deposition and high vacuum annealing in the Microfabrication Laboratory at California Polytechnic State University – San Luis Obispo. Characterization of the thin film by nanoindentation produced an elastic modulus of the thin film NiTi SMA with the developed processing parameters was 67.9 GPa with a hardness of 2.1 GPa. The measured thin film NiTi elastic modulus was greater than bulk NiTi of 40 GPa because of the residual stress from the deposition process. The shape memory effect was evaluated at the nanometer scale by measuring the nanoindents before and after thermally inducing a phase transformation. A maximum indentation depth recovery of 58% was measured upon the heat induced martensitic phase transformation. The low recovery was attributed to the high strain of 8% induced by the Berkovich tip. The effects of deposition power on the NiTi as-sputtered film stress, elastic modulus, hardness, and electrical conductivity were evaluated. At the highest sputtering deposition power of 450 Watts, an elastic modulus of 186 GPa with a hardness of 8.3 GPa was measured by nanoindentation. An increase in deposition power increased the residual film compressive stress, elastic modulus, and hardness while the electrical resistivity increased. The mechanisms for the measured properties are discussed in this thesis.

Significant drops in adhesion have been measured for copper and diamond like carbon (DLC) films with the introduction of water at the film/substrate interface. A 1 thick tungsten superlayer with high compressive residual stress was deposited on the films of interest to help induce interfacial debonding by indentation. Modifications were made to the superlayer indentation technique to introduce water at the interface while performing indents. Film adhesion dropped by a factor of 10 to 20 for the copper films and 50 to 60 for the DLC films. The reduction in adhesion is believed to be caused by a combination of lowering surface energy and a chemical reaction at the crack tip. When the film compressive residual stress is at least 4 times the critical buckling stress of a debonded film, telephone cord delaminations morphology can be observed. Delamination propagation has been induced in the past by applying a mechanical force to the film and similar results have been observed with the introduction of water. Crack propagation rates of 2 to 3 microns per second were measured for the DLC films with the introduction of water at the film/substrate interface. Telephone cord delaminations show potential for future use as microchannels in microfluidic devices and have shown excellent stability when manipulated with a microprobe to control fluid transport.

Nanostructured metallic multilayers (NMMs) are well-known for their high strength in smaller bilayer thicknesses. Six Al/Ti (NMM) with different individual layer thickness were tested for their mechanical hardness using a nanoindentation tool. Individual layer thicknesses were chosen carefully to cover the whole confined layer slip (CLS) model. Nano-hardness had a reverse relation with the square root of individual layer thickness and reached a steady state at ~ 5 nm bilayer thickness. Decreasing the layer bilayer thickness from ~ 104 nm to ~ 5 nm, improved the mechanical hardness up to ~ 101%. Residual stresses were measured using grazing incident X-ray diffraction (GIXRD). Effect of residual stress on atomic structure and dislocation propagation was then investigated by comparing the amount and type of stresses in both aluminum and titanium phases. Based on the gathered data from GIXRD scans tensile stress in Ti phases, and compressive stress in Al would increase the overall coherency of structure. Wear rate in coatings is highly dependent on design and architect of the structure. NMM coatings are known to have much better wear resistance compare to their monolithic constituent phases by introducing a reciprocal architect. In current study wear rate of two Al/Ti NMMs with individual layer thicknesses of ~ 2.5 nm and ~ 30 nm were examined under normal loads of 30 µN, 60 µN, and 93 µN. Wears strokes were performed in various cycles of 1, 2, 3, 4 5 and 10. Wear rates were then calculated by comparing the 3D imaging of sample topology before and after tests. Nano-hardness of samples was measured pre and post each cycle of wear using a nanoindentation tool. The microstructure of samples below the worn surface was then characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), focus ion beam (FIB) and an optical profilometer. Orientation mapping was performed to analyze the microstructure of layers beneath the nano indents. TEM imaging from the cross section of worn samples indicated severely plastically deformed layer (SPDL) below the worn surface. Shear bands and twins are visible after wear and below the worn surface. Decreasing the layer thickness from 30 nm to 2.5 nm resulted in ~ 5 time’s better wear resistance. Nanowear caused surface hardening which consequently increased nano hardness up to ~ 30% in the sample with 2.5 nm individual layer thickness. Increasing the interfaces density of NMMs will significantly improve the corrosion resistance of coating. Reciprocal layers and consequently interfaces will block the path of aggressive content toward the substrate. Corrosion rate evolution of Al/Ti multilayers was investigated through DC corrosion potentiodynamic test. Results seem to be very promising and demonstrate up to 30 times better corrosion resistance compared to conventional sputtered monolithic aluminum. Corrosion started in the form of pitting and then transformed to the localized galvanic corrosion. Decreasing the bilayer thickness from ~ 10.4 nm to ~ 5 nm will decrease the corrosion current density (icorr) of ~ 5.42 × 10-7 (A/cm2) to ~ 6.11 × 10-10 (A/cm2). No sign of corrosion has been seen in the sample with ~ 2.5 nm individual layer thickness. Further AFM and TEM analysis from surface and cross section of NMMs indicate that a more coherent layer by layer structure improves the corrosion rate. Interfaces have a significant role in blocking the pores and imperfections inside coating.

Lithium ion batteries (LIBs) have gained increasing popularity due to their high potential, low self-discharge, zero priming and minimal memory effect. However, the emergence of electrical vehicles and hybrid electrical vehicles in the automobile industry, where LIBs are predominantly in use, instilled a need to improve LIB batteries by experimenting with new materials. Graphite, the commonly used anode material for LIBs suffers from low theoretical capacity (372 mA h g-1) and torpid rate performance. Germanium (Ge) seems to be a promising substitute of carbon due to its high theoretical capacity, high Li+ diffusivity and electrical conductivity. However, Ge undergoes large volumetric change (±370%). This causes deboning of the thin film Ge electrode from the substrate current collector, causing a rapid decrease in the electrolytic performance. The process of ion beam mixing claims to have overcome this problem. In our current study, the adhesion strength of Ge thin film over Nickel (Ni) substrate (with and without ion beam mixing) is being measured using nanoindentation and the superlayer indentation test. Nanoindentation is one of the popular techniques to measure the mechanical properties and adhesion of thin film coatings. In this technique, a very small indenter of a desired geometry indents the film/substrate pair and the work of adhesion is calculated by knowing the plastic depth of indentation and the radius of indentation. Superlayer indentation is analogous to normal indentation but with a highly stressed superlayer on top to restrict the out-of-plane displacements, it reduces the plastic pile up around the indenter tip. The results from our study strongly suggest the possibility of dramatically increasing the adhesion strength by ion bombardment, which can be achieved by atomic level intermixing of the film/substrate pair. These, in turn, suggest that Ge could be an effective successor to graphite in the near future.

There is a technological need for hard thin films with high elastic modulus. Silicon Carbide (SiC) fulfills such requirements with a variety of applications in high temperature and MEMS devices. A detailed study of SiC thin films mechanical properties was performed by means of nanoindentation. The report is on the comparative studies of the mechanical properties of epitaxially grown cubic (3C) single crystalline and polycrystalline SiC thin films on Si substrates. The thickness of both the Single and polycrystalline SiC samples were around 1-2 µm. Under indentation loads below 500 µ-Newton both films exhibit Elastic contact without plastic deformation. Based on the nanoindentation results polycrystalline SiC thin films have an elastic modulus and hardness of 422 plus or minus 16 GPa and 32.69 plus or minus 3.218 GPa respectively, while single crystalline SiC films elastic modulus and hardness of 410 plus or minus 3.18 Gpa and 30 plus or minus 2.8 Gpa respectively. Fracture toughness experiments were also carried out using the nanoindentation technique and values were measured to be 1.48 plus or minus 0.6 GPa for polycrystalline SiC and 1.58 plus or minus 0.5 GPa for single crystal SiC, respectively. These results show that both polycrystalline SiC thin films and single crystal SiC more or less have similar properties. Hence both single crystal and polycrystalline SiC thin films have the capability of becoming strong contenders for MEMS applications, as well as hard and protective coatings for cutting tools and coatings for MEMS devices.

The deformation mechanisms operating in diamond-like carbon (DLC) coatings on (100) and (111) Si, has been investigated. The effect of coating thickness, indenter geometry, substrate orientation and deposition technique on the deformation of DLC coatings and the underlying substrate was studied by undertaking nanoindentation followed by subsurface microstructural characterization. Uncoated (111) Si was also investigated for comparison. The observed microstructural features were correlated to the indentation response of the coatings and compared with simulation studies, as well as observations on uncoated Si. In uncoated (111) Si, phase transformation was found to be responsible for the discontinuities in the load-displacement curves, similar to (100) Si. However, slip was activated on {311} planes instead of on {111} planes. Moreover, the density of defects was also significantly lower and their distribution asymmetric. The coatings were adherent, uniformly thick and completely amorphous. The load-displacement curves displayed several pop-ins and a pop-out, the indentation loads for the first pop-in and the pop-out depending primarily on the thickness of the coating. The coatings exhibited localized compressive deformation in the direction of loading without any through-thickness cracks. The extent of this localized deformation increased with indentation load. Hardness and thickness of the coatings and the geometry of the indenter influenced the magnitude of compressive strains. Harder and thinner coatings and a blunt indenter exhibited the minimum degree of deformation. Densification by rearrangement of molecules has been suggested as the mechanism responsible for plastic compression. At indentation loads corresponding to the first pop-in, (100) and (111) silicon substrates initially deformed by <111> and <311> slip respectively. Higher indentation loads caused phase transformation. Therefore, unlike in uncoated Si, dislocation nucleation in the Si substrate has been proposed as the mode responsible for the first pop-in. Subsequent pop-ins were attributed to further deformation by slip and twinning, phase transformation and extensive cracking (median and secondary cracks) of the substrate. The pop-out, however, was ascribed to phase transformation. Extensive deformation in the substrate, parallel to the interface, is attributed to the wider distribution of the stress brought about by the DLC coating. Good correlation was obtained between the nanoindentation response, microstructural features and simulation studies.

This thesis presents the results of a study focussed on the elucidation of the mechanisms responsible for determining the structural integrity of carbon coatings on ductile substrates. Through elucidation of these mechanisms, two different coating systems are designed; a multilayered coating and a functionally graded coating. While concentrating upon carbon coatings, the findings of this study are applicable to a broad range of hard coatings on ductile substrates. The thesis concludes with a chapter outlining a brief study of the effects of gold coatings on silicon under contact load at moderate temperatures to complement the major part of the thesis. Carbon coatings with differing mechanical properties were deposited using plasma enhanced chemical vapour deposition (PECVD), filtered assisted deposition (FAD) and magnetron sputtering deposition methods. Combinations of these techniques plus variation of deposition parameters enabled composite multilayered and functionally-graded coatings to also be deposited. Substrates were ductile metals; stainless steel and aluminium. Characterisation of the coating mechanical properties was undertaken using nanoindentation and nano-scratch tests. The same techniques were used to induce fracture within the coatings to allow subsequent analysis of the fracture mechanism. These were ascertained with the assistance of cross-sectional imaging of indents prepared using a focussed ion beam (FIB) mill and transmission electron microscopy (TEM) using specimen preparation techniques also utilising the focussed ion beam mill. A two dimensional axisymmetric finite element model (FEM) was built of the coating systems using the commercial software package, ANSYS. Substrate elastic-plastic properties were ascertained by calibrating load-displacement curves on substrate materials with the finite element model results. Utilising the simulation of spherical indentation, the distribution of stresses and the locations for fracture initiation were ascertained using finite element models. This enabled determination of the influence such factors as substrate mechanical properties, residual stresses in the coatings and importantly the variation of elastic properties of the different coating materials. Based upon the studies of monolithic coatings, simulations were undertaken on multilayer and functionally-graded coatings to optimise design of these coating types. Based on the results of the modelling, multilayered and functionally graded coatings were then deposited and mechanical testing undertaken to confirm the models. Three major crack types were observed to occur as the result of the spherical nanoindentation on the coatings; ring, radial and lateral cracks. Ring cracks were found to initiate from the top surface of the film, usually at some distance from the edge of the spherical contact. Radial cracks usually initiated from the interface between the coating and the substrate directly under the symmetry axis of indentation and propagated outwards in a non symmetrical star-like fashion. Lateral cracks formed either between layers in the multilayer coatings or at the interface with substrate. Ring and radial cracks were found to form upon loading whereas lateral cracks formed upon both loading and unloading depending upon the crack driving mechanism. Pop-in events in the load displacement indentation curve were found to be indicative of the formation of ring cracks, while the formation of the other types of cracks was not signified by pop-ins but rather by variations in the slope of the curve. The substrate yield strength was found to influence the initiation of all crack systems while compressive stresses in the coating were seen to only influence the formation of ring and radial cracks. However, it was also noted that the initiation of one form of crack tended to then hinder the subsequent formation of others. In multilayer coatings, the lateral cracks were suppressed, as opposed to the monolayer coating system, but a ring crack was observed. This drawback in the multilayer system was successfully addressed by the design of a graded coating having the highest Young??s modulus at the middle of the film thickness. In this coating, due to the graded nature of the elastic modulus, the stresses at the deleterious locations (top surface and interface) were guided toward the middle of coating and hence increased the load bearing capabilities. The effect of substrate roughness upon the subsequent surface roughness of the coating and also upon the fracture process of the coating during indentation was also investigated. For the coatings deposited on rough substrates, the radial cracks were observed to form initially and this eventfully delayed the initiation of ring cracks. Also the number of radial cracks observed at the interface was found to be proportional to the distribution of the interfacial asperities. In summary, the study elucidated the fracture mechanisms of monolayer, multilayer and graded carbon coatings on ductile substrates under uniaxial and sliding contact loading. The effects of the yield strength, surface roughness of the substrate, along with the residual stress and elastic modulus of the coatings on the fracture of coatings were investigated. The study utilised finite element modelling to explain the experiments observations and to design coating systems.

Group-III-nitride semiconductors (GaN, InGaN, and AlGaN) are important for the fabrication of a range of optoelectronic devices (such as blue-green light emitting diodes, laser diodes, and UV detectors) as well as devices for high-temperature/high-power electronics. In the fabrication of these devices, ion bombardment represents a very attractive technological tool. However, a successful application of ion implantation depends on an understanding of the effects of radiation damage. Hence, this thesis explores a number of fundamental aspects of radiation effects in wurtzite III-nitrides. Emphasis is given to an understanding of (i) the evolution of defect structures in III-nitrides during ion irradiation and (ii) the influence of ion bombardment on structural, mechanical, optical, and electrical properties of these materials. ¶ Structural characteristics of GaN bombarded with keV ions are studied by Rutherford backscattering/channeling (RBS/C) spectrometry and transmission electron microscopy (TEM). Results show that strong dynamic annealing leads to a complex dependence of the damage buildup on ion species with preferential surface disordering. Such preferential surface disordering is due to the formation of surface amorphous layers, attributed to the trapping of mobile point defects by the GaN surface. Planar defects are formed for a wide range of implant conditions during bombardment. For some irradiation regimes, bulk disorder saturates below the amorphization level, and, with increasing ion dose, amorphization proceeds layer-by-layer only from the GaN surface. In the case of light ions, chemical effects of implanted species can strongly affect damage buildup. For heavier ions, an increase in the density of collision cascades strongly increases the level of stable implantation-produced lattice disorder. Physical mechanisms of surface and bulk amorphization and various defect interaction processes in GaN are discussed. ¶ Structural studies by RBS/C, TEM, and atomic force microscopy (AFM) reveal anomalous swelling of implanted regions as a result of the formation of a porous structure of amorphous GaN. Results suggest that such a porous structure consists of N$_{2}$ gas bubbles embedded into a highly N-deficient amorphous GaN matrix. The evolution of the porous structure appears to be a result of stoichiometric imbalance, where N- and Ga-rich regions are produced by ion bombardment. Prior to amorphization, ion bombardment does not produce a porous structure due to efficient dynamic annealing in the crystalline phase. ¶ The influence of In and Al content on the accumulation of structural damage in InGaN and AlGaN under heavy-ion bombardment is studied by RBS/C and TEM. Results show that an increase in In concentration strongly suppresses dynamic annealing processes, while an increase in Al content dramatically enhances dynamic annealing. Lattice amorphization in AlN is not observed even for very large doses of keV heavy ions at -196 C. In contrast to the case of GaN, no preferential surface disordering is observed in InGaN, AlGaN, and AlN. Similar implantation-produced defect structures are revealed by TEM in GaN, InGaN, AlGaN, and AlN. ¶ The deformation behavior of GaN modified by ion bombardment is studied by spherical nanoindentation. Results show that implantation disorder significantly changes the mechanical properties of GaN. In particular, amorphous GaN exhibits plastic deformation even for very low loads with dramatically reduced values of hardness and Young's modulus compared to the values of as-grown GaN. Moreover, implantation-produced defects in crystalline GaN suppress the plastic component of deformation. ¶ The influence of ion-beam-produced lattice defects as well as a range of implanted species on the luminescence properties of GaN is studied by cathodoluminescence (CL). Results indicate that intrinsic lattice defects mainly act as nonradiative recombination centers and do not give rise to yellow luminescence (YL). Even relatively low dose keV light-ion bombardment results in a dramatic quenching of visible CL emission. Postimplantation annealing at temperatures up to 1050 C generally causes a partial recovery of measured CL intensities. However, CL depth profiles indicate that, in most cases, such a recovery results from CL emission from virgin GaN, beyond the implanted layer, due to a reduction in the extent of light absorption within the implanted layer. Experimental data also shows that H, C, and O are involved in the formation of YL. The chemical origin of YL is discussed based on experimental data. ¶ Finally, the evolution of sheet resistance of GaN epilayers irradiated with MeV light ions is studied {\it in-situ}. Results show that the threshold dose of electrical isolation linearly depends on the original free electron concentration and is inversely proportional to the number of atomic displacements produced by the ion beam. Furthermore, such isolation is stable to rapid thermal annealing at temperatures up to 900 C. Results also show that both implantation temperature and ion beam flux can affect the process of electrical isolation. This behavior is consistent with significant dynamic annealing, which suggests a scenario where the centers responsible for electrical isolation are defect clusters and/or antisite-related defects. A qualitative model is proposed to explain temperature and flux effects. ¶ The work presented in this thesis has resulted in the identification and understanding of a number of both fundamental and technologically important ion-beam processes in III-nitrides. Most of the phenomena investigated are related to the nature and effects of implantation damage, such as lattice amorphization, formation of planar defects, preferential surface disordering, porosity, decomposition, and quenching of CL. These effects are often technologically undesirable, and the work of this thesis has indicated, in some cases, how such effects can be minimized or controlled. However, the thesis has also investigated one example where irradiation-produced defects can be successfully applied for a technological benefit, namely for electrical isolation of GaN-based devices. Finally, results of this thesis will clearly stimulate further research both to probe some of the mechanisms for unusual ion-induced effects and also to develop processes to avoid or repair unwanted lattice damage produced by ion bombardment.

L'implantation ionique d'azote dans l'aluminium a pour conséquence d'améliorer certaines de ses propriétés superficielles et peut donc entre autre être utilisée comme traitement de surface pour les alliages d'aluminium. Cette étude fait suite au développement d'une nouvelle technologie d'implantation basée sur l'utilisation de microaccélérateurs de particules qui permettent l'implantation d'ions multichargés (jusqu'à N4+). L'objectif de la thèse a été dans un premier temps de cibler les paramètres d'implantation permettant d'obtenir les meilleurs résultats, notamment lors de tests de corrosion et d'usure. Une analyse microstructurale a été menée afin de comprendre les mécanismes rentrant en jeu dans le renforcement des surfaces implantées. On a ainsi, pu mettre en évidence la nécessité d'une interpénétration des couches nitrurées et oxydées pour une amélioration significative de la résistance aux sollicitations superficielles. Les mécanismes de durcissement ont également été étudiés ce qui a permis de mettre à jour un durcissement par écrouissage régi par effet Hall-Petch apparaissant lors de l'implantation. Une étude du comportement mécanique d'éprouvettes implantées a montré que malgré les faibles épaisseurs d'implantations (~0,5 µm) des effets pouvaient se faire sentir sur tout le volume des éprouvettes. Le comportement élastique ainsi que le mode d'endommagement de ces pièces ont en effet été modifiés après implantation.

Cette étude a pour but d'améliorer la compréhension et la modélisation du comportement en indentation de substrats de verre revêtus.<br /><br />Nous nous intéressons d'abord au contact élastique sur un substrat revêtu. Nous développons un algorithme semi-analytique permettant un calcul efficace de ce type de contacts. L'influence des désaccords de propriétés élastiques sur la réponse mécanique est étudiée. La méthode d'Oliver et Pharr induit une erreur sur la valeur du rayon de contact sur des systèmes revêtus. Nous proposons des pistes pour résoudre ce problème.<br /><br />Nous nous intéressons ensuite au comportement élastoplastique du verre de silice. Nous utilisons la microspectroscopie Raman pour évaluer la densité locale de ce matériau et ainsi cartographier la densification dans de la silice amorphe indentée et caractériser en pression hydrostatique de l'écrouissage de ce matériau. La prise en compte de cet écrouissage améliore les lois de comportement existantes. Nous étudions l'augmentation de la raideur de la silice amorphe avec sa densité. Nous utilisons la luminescence de Cr3+ pour étendre ces méthodes expérimentales à d'autres verres silicatés.