Low angle X-ray diffraction as a probe of reactions at buried interfaces and as characterization technique for thin films

In this paper we describe several uses of low angle X-ray diffraction to determine the structure and reactivity of thin films and interfaces, highlighting the sensitivity of these measurements to alignment of the sample with respect to the goniometer. A TiN film is used to demonstrate the ability of low angle diffraction to measure thickness without assuming optical constants or calibration data. The ability to extract density information via the critical angle and smoothness of deposited films from diffraction data is also detailed. Diffraction data from a silicon-germanium superlattice demonstrate the sensitivity of low angle diffraction to interfacial interdiffusion. Several features of this interdiffusion process are highlighted including the structural relaxation of the superlattice on initial annealing followed by the non-linear interdiffusion of the silicon and germanium layers. We only observe interdiffusion of the layers at higher temperatures and the crystallization of the thermodynamically stable solid solution rather than the elements as previously reported. The facile crystallization of the solid solution highlights the synthetic advantages of superlattices in avoiding stable reaction intermediates compared with the long annealing times required in conventional synthesis.