Direct Comparison of Core-Electron Binding Energies of Surface and Bulk Atoms of Ti, Cr, and Ni

A direct comparison has been made of electron-excited soft-x-ray appearance potentials, which are surface sensitive, and photon-excited Auger-electron appearance potentials, which are more characteristic of bulk atoms. A single tungsten emitter served as a reference for both measurements. The "surface chemical shifts" thus obtained for the $2p_{\frac{3}{2}}$ levels of Ti, Cr, and Ni are in reasonable agreement with predictions based on a muffin-tin approximation of overlapping one-electron potentials.