The finite element method is a promising mathematical technique that can be used to determine thin film mechanical properties from a composite film/substrate measurement. Others have used this technique to compute thin film properties and its use will probably increase due to the wide availability of finite element solvers and due to the robustness of the technique.

A critical component for using this technique is understanding the uncertainty in the computed thin film properties. The uncertainty will depend on several factors that include; the experimental parameters being matched, the film thickness, the indentation depth, the film properties, and the substrate properties. This paper will examine the effects of these parameters on computed thin film properties and will provide general guidelines for maximizing the accuracy of these computations.

Unique, microstructured thin films have been fabricated with the Glancing Angle Deposition (GLAD) technique. These porous, columnar thin films can be engineered with a diverse range of microstructures using a variety of materials to produce arrays of posts, helices, chevrons, periodically bent nematics (s-shapes), and many other configurations. The GLAD technique utilizes deposition at highly oblique incident angles onto unheated substrates to take advantage of shadowing and diffusion mechanisms. Due to the large incident angle, the shadowing effect is enhanced as areas of previous film growth physically shadow any subsequent flux, resulting in the evolution of isolated columns of material. And since the substrates are unheated, the diffusion length of the adatoms is limited and they do not fill in the voided areas produced from the shadowing process.

The helically structured thin films are of particular interest, as they resemble macroscopic springs and suggest that they might behave in an analogous manner. By optimizing the geometry of the “microsprings”, it is theoretically possible to create films that are capable of being actuated. Initial characterization of these chiral films has been underway, with some of the mechanical properties of these microsprings studied using atomic force microscopy (AFM) and nanoindentation. The study revealed that the spring constant of porous microspring films was twenty times lower than that of standard, dense films¹. Further investigation of these microstructured films is in progress, which is expected to reveal film properties that are unique to those fabricated by the GLAD technique and unlike those of traditional thin films.

¹M.W. Seto, K. Robbie, D. Vick, M.J. Brett, and L. Kuhn, "Mechanical Response of Thin Films with Helical Microstructures", J. Vac. Sci. Technol., B 17(5), 1999, pp. 2172-217.

Chromium nitride (Cr-N) coatings have received increased attention for tribological applications due to their favorable properties including wear resistance, toughness and oxidation resistance. These properties, in turn, can be strongly influenced by the coating microstructure and residual stress resulting from deposition and subsequent processing operations. In this study these microstructural-property correlations are investigated in Cr-N coatings grown by arc-evaporation.

Previous investigations on these coatings have identified the dependence of the microstructure and residual stress on both incident ion energy during growth and ex-situ thermal annealing. Prominent features during growth include formation of metastable amounts of the (textured) cubic CrN phase, and high levels of compressive residual stress and defect density. During annealing to 550°C the residual stress and defect density decrease substantially, accompanied by a diffusion-based CrN to Cr₂N phase transformation.

The effects of these microstructural modifications on the elastic-plastic and fracture properties of the coatings are quantatively evaluated. Significant variations in these properties, as determined from a combination of nanoindentation, surface acoustic wave and scratch techniques, occur after annealing. These changes are then correlated to the Cr-N microstructure in order to better understand coating performance. For example, it is shown that hard and adherent coatings can be attained after annealing through the formation of nano-scale equiaxed grains and a diffusion-bonded interface.