ENERGY SHIFT OF THE CU L(3)M(4,5)M(4,5) AUGER LINE EXCITED BY PROTON IMPACT ON CU(110) - ENHANCED ELECTRON CORRELATIONS AT THE SURFACE

CuL(3)M(4,5)M(4,5) Auger spectra excited by impact of 1.0-MeV protons on Cu(110) were measured. In the case of grazing incidence angles, a s hift of the Auger line to higher kinetic energies was observed. This i s attributed to a surface effect; The observed shift is interpreted wi thin the Cini-Sawatzky theory. Taking into account the surface core-le vel shift and the surface shift of the center of gravity of the valenc e band only is not sufficient to explain the observed shift of the Aug er line, We find evidence that the shift is partly due to-a change of the on-site Coulomb interaction U at the very surface. A rough estimat ion shows U to be increased by less than 0.6 eV at the surface when co mpared with the bulk.