Why changes in bond lengths and cohesion lead to core-level shifts in metals, and consequences for the spatial difference method

In metals, the chemical shifts of core-level energy loss spectra are largel y determined, not by charge transfers, but instead by valence band shifts. The valence band shifts in turn are determined by changes in bandwidth, whi ch result from changes in the type, number and distance to neighboring atom s. The core-level shifts tracks the valence-band shifts to within 0.1 eV, t hus providing information on the occupied electronic states. As a consequen ce, core-level shifts are almost unavoidable at interfaces and cannot be ig nored when analyzing data obtained by the 'spatial' difference method. Core -level shifts introduce first-derivative-like features in spatial differenc e spectra, that under typical conditions will be larger than the changes in energy-loss fine structure. Fortunately, it is far simpler to connect the core-level shifts to changes in cohesive energy than parameterizations of t he fine structure, such as charge transfers. Reinterpreting spatial differe nce measurements of Cu : Bi, Fe : B and Fe : P grain boundaries as arising from core-level shifts may reconcile the experimental measurements with exi sting electronic structure calculations. (C) 1999 Elsevier Science B.V. All rights reserved.