Depth Resolved Structural Studies in Multilayers Using X-ray Standing Waves

X-ray based characterization techniques are powerful tools for the study of atomic scale structure of materials. However, high penetrating power of X-rays make them less suitable for depth selective studies, as required in the characterization of multilayer structures. In the present work, it is shown that depth selectivity of the techniques like, X-ray fluorescence, X-ray absorption spectroscopy and nuclear resonance fluorescence can be greatly enhanced by generating X-ray standing waves inside the multilayer structure. The concentration profiles of various elements can be obtained with a depth resolution of the order of 0.1 nm. Depth dependent information about the local structure around a given atom can be obtained from XAFS under standing wave conditions. It is demonstrated that detection of nuclear resonance fluorescence by tuning the energy of the incident X-rays to a Mössbauer transition can yield depth profile of a particular isotope, and can be used for self-diffusion studies. The techniques of X-ray reflectivity and conversion electron Mössbauer spectroscopy are used to provide useful complementary information.