Analysis of MIES and UPS data of LiF and NaCl

Abstract Published electron energy spectra of LiF and NaCl surfaces taken by HeI UPS and by He*(2 3 S) MIES are reanalyzed. By simulation of the spectra on the basis of the calculated bandstructure, it is possible to establish the energy position of the top of the valence band on the energy scale of the experimental spectra. It is found that the MIE spectra are shifted by several 100 meV to higher electron energies compared to UPS. Based on a hypothesis presented by Kuchitsu and coworkers in 1980, this can be explained by the localization of the created hole state in the topmost atomic layer of the crystal surface. The difference between surface and bulk Madelung energy plays two roles: firstly, it explains the observed energy shift in MIES, and secondly, it seems to explain the long lifetime of a surface hole state in ionic insulators.