Coadsorption of CO and K on Ni(100) II. XPS, UPS, Δφ and ELS studies

Abstract

Abstract The coadsorption of carbon monoxide and potassium on Ni(100) has been investigated using X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS), electron energy loss spectroscopy (ELS) and change-of-work-function measurement (Δφ). The binding energies (BE's) of C(1s) and O(1s) decrease with increasing potassium coverage (θK), while the CO orbital BE's 1 gp and 4 gs increase and the 5 gs remains fixed. With increasing θK the energy separation between the CO-Ni derived 2φ orbitals decreases. Δφ indicates a larger effective dipole moment for CO at low θK than on clean Ni(100). A model is suggested involving a CO buffering effect on K-K repulsion, resulting with a stabilization of the K adatoms and a polarization of CO valence orbitals. Enhanced Ni-to-CO(2 gp) charge transfer is induced by electrostatic field effects from the K adatoms shifting the CO(2 gp) level closer to the metal Fermi level.