Indentation of strained silicate-glass films on alumina substrates

The development of the technique presented in this paper provides a new method of studying residual stresses in thin films on bulk substrates. It has been demonstrated that with a relatively simple deformation geometry, the behavior of thin films on substrates can be studied systematically from both morphological and mechanical prospective. Particular aspects of the technique which have been demonstrated are as follows: • The method proposed hi the paper offers a new approach of introducing precisely controlled residual stresses into thin films without modifying either the film's chemical composition or changing the deposition conditions, particularly, deposition environment, film thickness, growth rate or temperature. • A straightforward experimental procedure allows to generate a wide range of residual stresses (from a tensile stress to a compressive stress up to the stresses causing the film's failure). The stresses can be related to the changes observable in the load-displacement behavior and the film morphology. • A direct comparison in film's micromechanical behavior can be offered since both strained and unstrained films were grown for a single deposition run. To assess the variations in film's mechanical behavior and to detect the influence of the applied stress in the thin films, on the hardness and the elastic modulus well-developed nanoindentation methods were employed. • The experimental data demonstrate that the well-known analysis procedure for determining thin-film hardness and Young's modulus from nanoindentation data is deficient and can be strongly affected by the presence residual stresses. As an example of this approach, preliminary results have been shown for anorthite glass films on single-crystal alumina substrates. It is proposed that the observed changes in the surface morphology of the film, combined with nanoindentation data in this study, will give an improved understanding of the mechanisms of thin-film relaxation on substrates.