Theory of thin-film orientation by ion bombardment during deposition

We study the development of orientational order in thin films grown with off-normal incidence ion bombardment during deposition. The overall orientational order in our model results from the dependence of the sputtering yield on grain orientation. We demonstrate that the degree of orientational order at the surface of a thick film grows slowly with increasing ion flux until, at a critical value of the flux, it begins to rise more steeply and then saturates at its maximum value. The time needed to approach the thick-film limit displays a peak as the ion flux is varied. We compare our work with the experimental results of Yu et al. [Appl. Phys. Lett. 47, 932 (1985)] and use our results to show how the deposition technique can be optimized.