THEORETICAL SURFACE CORE-LEVEL SHIFTS FOR BE(0001)

Core-ionization potentials (CIP's) are computed for Be(0001). Three core features are observed in corresponding photoelectron spectra, with CIP's shifted relative to the bulk core level by -0.825, -0.570, and -0.265 eV. The computed CIP shifts for the outer and subsurface layers, -0.60 and -0.29 eV, respectively, agree with the latter two of these. It is surmised that the -0.825-eV shift is associated with a surface defect. The negative signs of the Be(0001) surface core-level shifts do not fit into the thermochemical picture widely used to explain CIP shifts. The reason is that a core-ionized Be atom is too small to bond effectively to the remainder of the unrelaxed Be lattice.