X-Ray Stress Gradient Analysis in Thin Layers — Problems and Attempts at Their Solution

Due to the small diffracting volume as well as texture, X-ray diffraction at thin polycrystalline coatings often leads to line profiles of rather weak intensity, and therefore, stress analysis involves a series of difficulties. This applies especially to non-uniform stress distributions within layers, the thickness of which is small with respect to the penetration depth τ of the X-rays. In order to compare several methods of X-ray stress analysis concerning their suitability for the detection of stress gradients in thin layers, the shape and the position of the diffraction lines are calculated for simulated stress profiles as a function of the layer thickness and the diffraction geometry. The best results in stress distribution evaluation are achieved, if the deformation depth profiles εφψ(τ) are obtained at grazing incidence in the scattering vector mode, where τ is adjusted by rotating the sample around the normal of the reflecting lattice planes, Nh.