Fracture-EXAFS is a technique, proposed here for the first time, which combines an appropriate mechanical test with EXAFS analysis to investigate the atomic processes involved in the fracture process. Fracture-EXAFS builds upon the fracture-Auger electron spectroscopy technique, which was used to study the elemental composition of fracture surfaces, and has yielded significant insight into phenomena such as grain boundary embrittlement and composite interface fracture. Extended X-ray Absorption Fine Structure (EXAFS) analysis yields structural, as well as chemical information. The identity, coordination number, position and degree of disorder of atoms in the vicinity of interfaces and surfaces can be determined. Thus, EXAFS comparison of the imminent (latent) fracture surface to the fracture surface can yield structural, as well as chemical information about the fracture process. In this preliminary report, emphasis will be given to the application of Fracture-EXAFS to the study of interfaces in thin films. Discussion will also include the use of Fracture-EXAFS to study grain boundaries in polycrystalline materials.

A method has been developed of separating the porous film produced by anodizing aluminium from its substrate. Such films have a honeycomb morphology with pores that open at both surfaces. They are composed of essentially anhydrous alumina doped with acid anion from the anodizing electrolyte, and are electron diffraction insensitive. A geometrical model has been developed that describes how the pore morphology is determined by the anodizing voltage. Using this model, expressions are derived that relate cell dimensions to voltage-determined parameters and bulk properties such as porosity.

The flexural modulus and tensile strength of honeycombs have been modelled by considering bending moments experienced by the cell walls. Thus, the properties were expressed in terms of cell dimensions. Here, the anodic film and honeycomb models are combined. These are used to analyze the mechanical properties of the films as determined by the anodizing parameters. A critical crack size is predicted and compared with the results of microstructural examinations. Good agreement is shown. Assumptions behind these findings and the implications arising are discussed.

The “supermodulus effect” has been reported as an anomalous increase of as much as several hundred percent in the elastic moduli of compositionally-modulated thin metal films in a narrow range of modulation wavelength. The direct measurement of this effect has, however, been limited due to the very small dimensions of the test material. The mechanical properties of compositionally-modulated Au-Ni thin films (one of the first systems in which the supermodulus effect was reported) were studied on their substrates by indentation and microbeam-deflection techniques using a Nanoindenter. The films were fabricated by alternately sputtering Au and Ni onto [100] Si substrates for the indentation tests and onto prefabricated SiO2 cantilever beams with an initial Cr layer (for adhesion) for the beam deflection tests. All of the films have strong [111] textures and exhibit the structural characteristics of the films for which the modulus enhancement was reported. In particular, an increase in the average lattice parameter normal to the plane of the film over a narrow range of modulation wavelengths near 2 nm was noted. The modulation wavelengths range from 0.8 to 4.5 nm. The results from both indentation and microbeam deflection tests reveal no unusual plastic or elastic properties in these samples.

Artificially multilayered copper/nickel thin films with bilayer repeat lengths between 1.6 and 12 nm were produced by ion beam sputtering. The mechanical properties of these films were investigated by low load microhardness and nanoindentation (force versus depth) techniques. It was found that none of the films displayed bilayer repeat length dependent enhanced elastic behavior (the supermodulus effect) as measured during unloading in the nanoindenter. However, enhancements in hardness, as measured by both the nanoindenter and the low load microhardness tester, were observed in films with small bilayer repeat lengths. These measurements displayed a Hall-Petch-type relationship, using the individual layer thickness (equal to half the bilayer repeat length) as the characteristic “grain size.” This hardness behavior can be understood in terms of a mechanism involving dislocation pinning at the interfaces analogous to the mechanism of grain boundary hardening.

A 900 Å as-deposited multilayered structure of alternating Fe and Ti on hardened tool steel has been examined for tribological and mechanical properties. The multilayer in contact with a 52100 steel ball counter surface possessed a 0.16 friction coefficient and showed good wear character after 1000 cycles in pin-on-disk experiments. Nanoindentation experiments show a 20 % increase in hardness for material in the wear track. Electron microscopy data suggests that the as-deposited bcc-Fe plus hcp-Ti multilayer composite transforms to a nanocrystalline alloy plus bcc-Fe by solid state reaction during pin-on-disk friction and wear test. The low friction observed in these surface films is attributed to the formation of a hard nanocrystalline alloy and improved interlayer and film/substrate adhesion which result during solid state reaction.

We have investigated the hardness and tribological properties of Cu/TiB2 multilayer structures deposited on substrates of tempered martensitic steel. Films of Cu and TiB2 were also deposited as hardness standards. The wear properties of the films were found to be poor, because of lack of adhesion. However, the films do appear to have good fracture toughness. The hardness of the multilayer was 18% greater than that predicted by the law of mixtures applied to the reference standards and, when corrected for variations in substrate hardness, very nearly equal to that of the TiB2 film. Irradiation by 400 keY Ne-ions to doses of 1.0, 6.0, and 12×1015 ion/cm2 results in a slight hardening of the multilayer. The structure was found to have excellent stability against radiation damage.

The mechanisms and kinetics of forming misfit dislocations in heteroepitaxial films are studied. The critical thickness for misfit dislocation formation can be found by considering the incremental extension of a misfit dislocation by the movement of a “threading” dislocation segment that extends from the film/substrate interface to the free surface of the film. This same mechanism allows one to examine the kinetics of dislocation motion and to illuminate the importance of dislocation nucleation and multiplication in strain relaxation. The effects of unstrained epitaxial capping layers on these processes are also considered. The major effects of such capping layers are to inhibit dislocation nucleation and multiplication. The effect of the capping layer on the velocity of the “threading” dislocation is shown to be small by comparison.

A new substrate curvature technique for measuring the strain and studying the kinetics of strain relaxation in heteroepitaxial films is also briefly described.

A brief study of the microhardness of nanocomposite coatings fabricated by a new technique is reported. The new fabrication technique utilizes sputtering at high pressures in a thermal gradient to produce nanometer-size particles, which are then embedded in a matrix produced by conventional sputtering. The microstructures and microhardness of nanocomposite coatings of Al matrix reinforced by Mo particles (grain diameter ranging from 7 to 20 nm) are reported.

Thin ceramic coatings have been used in tribological applications for some time because their high defect densities and small grain size leads to a very hard, wear-resistant surface. However it is not sufficient to look at properties such as hardness in isolation when considering the selection of a coating for a given engineering application as other properties such as residual stress or adhesion may be equally important. In fact it is central to the continued development of advanced coating technologies to understand the inter-relationship between the important properties of the coating/substrate system (residual stress, hardness, adhesion etc.) and coating microstructure particularly as this can be controlled to a certain extent by the choice of deposition technology and processing parameters. By using PVD titanium nitride as an example, this paper reviews the potential for microstructural control using current physical vapour deposition (PVD) processes and shows how the microstructure of the coating is important in dictating its mechanical properties. These properties and others which still need to be measured are discussed and the potential for designing with coatings assessed in the light of current understanding.

Photoreflectance (PR) was used to study crystalline quality and stress in silicon films on insulator. The position and amplitude of the 3.4 eV PR silicon structure was monitored for both MBE silicon on sapphire (SOS) and SIMOX structures. The SOS film thicknesses ranged from 6 to 4000 nm. The shift in energy of the 3.4 eV structure from its bulk position is dependent on the sample thickness and on the strain in the films. In the SIMOX case, the amplitude of the 3.4 eV PR signal provided information about the crystalline quality of the top silicon layer for a set of six samples, each one removed at a different step of a process involving three implantation-anneal cycles. In this case the PR signal appeared to deteriorate with the each cycle undergone by the samples. Further investigations are needed to resolve the discrepancy bet ween these SOS results and the ones obtained in an earlier set of measurements.

We have used Brillouin scattering to study the dependence of the elastic constants of uniaxial polymeric Langmuir-Blodgett thin films on the thickness of the polymeric molecule monolayers. With increasing monolayer thickness, an overall decrease in the elastic constants and an increase in the refractive index n33 was observed.