Surface composition of clean and oxidized Pd75Ag25(100) from photoelectron spectroscopy and density functional theory calculations

► The clean Pd75Ag25(100) surface exhibits a positive surface core level shift in Pd 3d core level photoemission spectra. ► This shift is found to be the signature of Pd embedded in a Ag rich surface layer. ► Oxidation of the Pd75Ag25(100) surface results in a 5×5R27°-O structure. ► The oxide structure is similar to the one seen for Pd(100).