Direction-dependent grain interaction in nickel and copper thin films, analysed by X-ray diffraction

The elastic grain interaction due to surface anisotropy and morphological ('grain-shape') texture in real, polycrystalline materials has been considered. It has been demonstrated for the first time that the effect of surface anisotropy and morphological texture on polycrystal elastic behaviour can be distinguished in a diffraction stress analysis by evaluating lattice strain measurements from multiple reflections simultaneously. Non-linear ε-sin2ψ plots (i.e., plots of the lattice strain ε versus sin2ψ, where ψ is the angle between the surface normal of the specimen and the diffraction vector) have been obtained for 0 0 l and h h h reflections in the diffraction stress analysis of sputter-deposited nickel and copper thin films. Such observed non-linearities can only be interpreted on the basis of a direction-dependent grain interaction due to surface anisotropy or morphological (grain-shape) texture. For the specimens investigated, it has been found that surface anisotropy is the dominant factor causing the observed non-linearities in the ε-sin2ψ plots. These findings have been confirmed by focused ion beam microscopy: The specimens investigated do not exhibit a grain-shape texture.