ELECTRONIC PROPERTIES OF BARIUM ULTRATHIN LAYERS ON THE Ni(110) SURFACE

Abstract

In this paper, we study the adsorption of Ba on the Ni (110) surface at room temperature. The investigation takes place mainly by soft X-ray photoelectron spectroscopy measurements. At low coverage (<0.5 ML ), the Ba adatoms are in a partially ionic state, whereas at higher coverage, the barium overlayer becomes metallic. The nonmetal to metal transition is characterized by a new Ba 4d doublet appearing at higher binding energy. This more bound Ba 4d core state is attributed to initial state changes of the electrostatic potential at the atomic core region, due to changes in the hybridization of the Ba atoms from Ba 5d with Ni 3d, to Ba 5d, 6s and 6p states in the metallic phase. The latter states are more spatially extended than the Ba 5d ones, overlapping with the Ni 3d orbitals in the nonmetal and therefore lead to a reduced potential at the core electrons. A strong effect on the Ba 4d binding energy shifts, due to the surface dipole induced by the adsorbate itself, was observed.