ADLAYER CORE-LEVEL SHIFTS OF RANDOM METAL OVERLAYERS ON TRANSITION-METAL SUBSTRATES

We calculate the difference of the ionization energies of a core elect ron of a surface alloy, i.e., a B atom in a A(1-x)B(x) overlayer on a fee B(001) substrate, and a core electron of the clean fee B(001) surf ace using density-functional theory. We analyze the initial-state cont ributions and the screening effects induced by the core hole, and stud y the influence of the alloy composition for a number of noble metal-t ransition metal systems. Our analysis clearly indicates the importance of final-state screening effects for the interpretation of measured c ore-level shifts. Calculated deviations from the initial-state trends are explained in terms of the change of inter- and intra-atomic screen ing upon alloying. A possible role of alloying on the chemical reactiv ity of metal surfaces is discussed.