Electron donor–electron acceptor interactions in surface metal–metal bonds: The Cu/Re(0001) and Pd/Re(0001) systems

Abstract

The interaction of Cu and Pd with Re(0001) has been examined by means of temperature programmed desorption and x‐ray photoelectron spectroscopy. A Cu monolayer desorbs from Re(0001) at a temperature of 1180 K and has an electron density similar to that of the surface atoms of Cu(100). Pd adatoms on Re(0001) are electronically perturbed with respect to surface atoms of Pd(100), desorbing at a temperature of 1450 K. By comparison of these results with those previously presented in the literature for Pd and Cu adlayers, we found that there is a correlation between the electronic perturbations in the adlayers, the strength of the admetal–substrate bonds, and the ability of the adatoms to chemisorb CO. The results indicate that formation of a surface metal–metal bond leads to a gain in electrons by the element initially having the larger fraction of empty states in its valence band. This behavior is contrary to that observed in bulk alloys, indicating that the electronegativities of the surface atoms are substantially different from those of the bulk. A method to establish a scale of surface electronegativities is proposed.