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 spectroscop y (LEIS), Auger electron spectroscopy (AES), scanning tunnelling microscopy (STM), X-ray photoelectron diffraction (XPD) and ab initio local density f unctional 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 h igher temperatures vanadium diffuses into subsurface layers and, at a tempe rature of 300 degrees C, only a small amount of vanadium is observed in the topmost layer. STM revealed the formation of a (root 3 x root 3)R30 degree s superstructure and XPD measurements demonstrated that this structure is d ue to vanadium atoms incorporated in the second layer. This finding is conf irmed by ab initio calculations. A model for the (root 3 x root 3)R30 degre es structure based on the experiments and the ab initio calculations is giv en. (C) 2000 Elsevier Science B.V. All rights reserved.