Structure and Properties of Surface Layers: X-ray Diffraction Studies

Abstract

Because X-rays are strongly absorbed on propagation through solid material, X-ray diffraction analysis can be fruitfully applied in the study of surface layers. After a brief discussion of some aspects of X-ray diffraction analysis of surface layers, attention is focussed on investigations of stress development and interdiffusion in surface layers. The behaviour of surface layers depends largely on their state of (residual) macro- and microstress. The development and possible relaxation of macrostress in surface layers can originate from the thermally imposed difference in shrink or expansion between layer and substrate, from developing concentration profiles and from structural changes, in particular phase transformations. Diffusion processes in multilayers, composed of alternately stacked sublayers of elements A and B, are highly affected by the multitude of interfaces and therefore differ from those in bulk material. The effective diffusion coefficients can be determined from the decrease of the intensity of the reflections corresponding to the composition-modulation period [so-called (000) satellites], and the change of the integrated intensities of reflections from produced or retained crystalline components. Examples of interdiffusion in an amorphous multilayer (in conjunction with structural relaxation) and in a crystalline multilayer (leading to amorphisation) are presented.