X-ray absorption fine structure study of short-range order of iron in Fe/Al multilayers

Abstract

Results of quantitative analysis of fluorescence x-ray absorption fine structure (XAFS) experiments at the Fe–K absorption edge are presented for a 6*(4.3 nm Fe/10.4 nm Al) multilayer prepared by pulsed laser deposition. Fluorescence XAFS experiments have been combined with excitation of x-ray standing waves. This combination in one experiment allowed for a depth-controlled excitation of Fe fluorescence and hence for a depth-resolved analysis of short-range order. Depth-resolved analysis showed that instead of sharp Fe/Al or Al/Fe interfaces extended interlayer regions exist. The structure retained that of bulk α-Fe. In the upper half of the Fe layer 37 at. % Al as nearest and next nearest neighbors of Fe were found, whereas in the lower half 80 at. % Al atoms occur. Thus the Fe/Al interface (deposition of Fe on Al) should be characterized by an intermixing zone significantly larger in comparison to that of the Al/Fe interface (deposition of Al on Fe). By conventional XAFS measurement carried out at a fixed angle of incidence of the exciting beam an average Fe neighborhood for the entire Fe layer of 58 at. % Al atoms was found. This value agrees with the average obtained when the analysis of the layer was performed separately for two sublayers by shifting the wave field through the layer.