Surface and subsurface alloy formation of vanadium on Pd(111)

We have studied the submonolayer growth of vanadium on the Pd(111) surface at different substrate temperatures. By means of low-energy ion spectroscopy (LEIS), Auger electron spectroscopy (AES) scanning tunnelling microscopy (STM), X-ray photoelectron diffraction (XPD) and ab initio local density functional calculation we find that, at room temperature, deposited vanadium atoms substitute surface palladium atoms. In addition, islands are formed on the surface that consist mostly of the substituted palladium atoms. At higher temperatures vanadium diffuses into subsurface layers and, at a temperature of 300°C, only a small amount of vanadium is observed in the topmost layer. STM revealed the formation of a (3×3)R30° superstructure and XPD measurements demonstrated that this structure is due to vanadium atoms incorporated in the second layer. This finding is confirmed by ab initio calculations. A model for the (3×3)R30° structure based on the experiments and the ab initio calculations is given.