Effect of Stress on the Physical Properties of Thin Films

Residual stresses are almost always present in thin films; the magnitude of the stress (tensile or compressive) can be as small as 107 or as large as 1010 dyn/cm2. The stress in fine-grained polycrystalline films is generally isotropic in the plane of the film, and has no stress component perpendicular to the film plane. In such films there is then an isotropic strain in the film plane with a Poisson’s strain normal to the plane. For single crystal films the strain anisotropy will depend on the orientation of the film axes with respect to the substrate. In either case these strains induce an anisotropy and changes in the physical properties of the film. As examples of the effect of stress, the changes in magnetic and superconducting transition temperatures, and the induced magnetic, resistive, and optical anisotropies will be discussed.