Surface composition of clean and oxidized Pd_(75)Ag_(25)(100) from photoelectron spectroscopy and density functional theory calculations

摘要

High resolution photoelectron spectroscopy and density functional theory calculations have been used to study the composition of clean and oxidized Pd_(75)Ag_(25)(100). The results for the clean surface confirm earlier reports of surface segregation by Wouda et al. (1998), where the top most layers are rich in Ag. The Pd 3d core level component from the surface region is observed at higher binding energies than the contribution from the bulk which is found to be a signature of Pd embedded in Ag. Low energy electron diffraction and scanning tunneling microscopy measurements reveal that oxidation of the Pd_(75)Ag_(25)(100) surface results in a (5~(1/2)× 5~(1/2)) R27°-O structure similar to the one reported for Pd(lOO). The calculations suggest that the stable structure is a PdO( 101) monolayer supported on a (100) surface rich in Ag at the interface to the stoichiomet-ric alloy. The calculated core level shifts for the oxidized surface are in good agreement with the experimental observations.