Probing atomic environments in alloys by electron spectroscopy

In alloys exhibiting substitutional disorder, the variety of atomic environments manifests itself as a "disorder broadening" in their core-level binding-energy spectra. Disorder broadening can be measured experimentally and, in principle, can be used to deduce information about specific atomic environments within a sample. However, progress in this endeavor is hampered by the lack of a model for this phenomenon which can treat complex systems. In this work we describe such a model. The model is used to elucidate the relationship between charge transfer, atomic environment, and disorder broadening in complex systems, with a focus on the problem of characterizing the interface quality of CuNi multilayers. We also validate the model against the results of ab initio electronic-structure calculations. Several counterintuitive aspects of the disorder-broadening phenomenon are uncovered, an understanding of which is essential for the correct interpretation of experimental results. For instance, it is shown that systems with inhomogeneous concentration profiles can exhibit disorder broadenings significantly larger than random alloys. Furthermore, in some systems a "disorder narrowing" is even possible.