ALLOYING OF THIN AG AND AU FILMS ON PD(111) STUDIED BY HIGH-RESOLUTION PHOTOELECTRON-SPECTROSCOPY OF SURFACE-STATES

Alloy formation by annealing of thin Ag and Au films on Pd(111) is stu died by high-resolution ultraviolet and two-photon photoelectron spect roscopy of surface states. Changes in the composition of the top layer of the surface alloys are reflected in the energy of the surface stat es. Above an annealing temperature of 500 K on both systems, the cryst al-induced surface state shifts continuously from the occupied state o f the adsorbate to the unoccupied state of the substrate. The continuo us shift reflects the variable composition of the alloys in the surfac e region which depends on the initial coverage and the annealing tempe rature. The spectroscopy of the unoccupied image states permits the in vestigation of growth and morphology of deposited metal layers. Three- dimensional island growth, layer-by-layer growth, and surface alloy fo rmation with metastable surface configurations and diffusion of the ov erlayer material into the bulk are identified.