Non-local Effects on Oxygen-Induced Surface Core Level Shifts of Re(0001)

The electronic structure of clean and oxygen-covered Re(0001) was investigated by combining high energy resolution core level photoelectron spectroscopy and density functional theory. For the clean surface, we detect two distinct Re 4f7/2 components shifted by 95 meV, which we ascribe to photoemission from the bulk and the top layer of the crystal. Oxygen adsorption at room temperature leads to the appearance of new core level components, which we associate to non-equivalent Re atoms from the topmost layer. In addition to the linear relationship between oxygen-induced core level shifts and number of O–Re bonds, we find that the binding energy shift also depends on the number of oxygen atoms at second and third nearest neighbor positions. This non-local effect is discussed in terms of 5d band center shift and of charge transfer between the metallic substrate and the O atoms.