SURFACE HYBRIDIZATION SHIFT OF THE EMPTY F-SPECTRAL-FUNCTION IN CE COMPOUNDS

Surface effects are detected between the f spectral functions obtained from UV and X-ray inverse photoemission spectra of a number of Ce com pounds. They are: a variation of the I(f(1))/I(f(2)) intensity ratio, which indicates the presence of a less hybridized surface layer compar ed to the bulk, and a surface-to-bulk shift of the f(2) component, whi ch is larger than the expected surface core level shift as measured on isostructural Lu compounds. The extra shift (up to 0.3 eV) is interpr eted as a hybridization effect in agreement with theoretical calculati ons. Some consequences on the on-site f-f correlation energy at the su rface are drawn.