Depth-resolved x-ray absorption fine structure study of Fe∕Si interfaces using x-ray standing waves

X-ray standing waves generated by total external reflection (TER) from an underlayer of Au have been used to perform depth resolved x-ray absorption fine structure (XAFS) studies on a Si∕Fe∕Si trilayer in which intermixing has been induced by irradiation with 100 MeV Au ions. It is demonstrated that the technique has a sufficient depth resolution so as to elucidate the depth distribution of various phases formed across the interfaces. Irradiation to a fluence of 1×1013 ions∕cm2 results in complete mixing of the Fe layer. It is observed that in the center of the intermixed layer, the short-range order around Fe ions is similar to the FeSi phase. Moving away from the center, Si concentration increases and the local structure around Fe becomes similar to that of the FeSi2 phase. On the other hand, depth integrated XAFS data could have been interpreted in terms of a homogeneous FeSi2 type of short-range order in the system. Thus, the depth selectivity achieved using TER standing waves combined with the sensitivity of XAFS to local order around a specific element makes it a valuable tool for studying layered materials.