Chapter VI - Stresses in thin films

Abstract

This chapter discusses the measured values of the intrinsic tensile stress molecular dynamics (MD) simulations. There are several factors that contribute to the tensile stress on a film. One is the long-range interaction of the assumed inter atomic potential that spans voids of shorter width. Another is the contribution of the surface tension of the enclosed cylindrical void surfaces, a possibility first suggested by Heavens and Smith. The stress increment because of this source is proportional to f/(1–f), where f is the void volume fraction, void surface energy, and is inversely proportional to the pore radius. The proportionality constant depends upon void morphology, and its magnitude is on the order of unity. Because porosity is observed in films in the zone, it is apparent that there still exist internal surface area and energy in the film. To the extent that voids exist, that there is space between columns not filled by cohering atoms, the magnitude of the average tensile stress in the films must be less than that deduced from the Hoffman analysis.