CORE-LEVEL SHIFTS IN AMORPHOUS TRANSITION-METAL TIN ALLOYS

X-ray and UV photoemission data are presented for core level binding energy shifts in amorphous TM-Sn (TM = Fe, Co, Ni, Pd) films prepared in situ at low temperature by means of a vapour quenching technique. The experimental results are compared to predictions based on the thermodynamical model of Martensson and Johansson using the Born-Haber cycle and the equivalent core approximation. The overall good agreement found between theory and experiment emphasizes the strong influence of the conduction electrons in the photoionization process. It is observed that relaxation effects and screening of the final core hole state can result in binding energy shifts of the same order of magnitude as those of the ground state due to alloying. As a consequence, photoemission core level binding energies in amorphous alloys generally cannot be interpreted within the ground state picture, but have to be corrected for final state contributions.