Adsorption of CO on a Ni(111) surface

Abstract

Carbon monoxide adsorbed on Ni(111) forms around θ = 1/3 an ordered √3 × √3/R 30c structure whose unit cell is continuously compressed upon further increasing the coverage until at saturation (θ=0.53 corresponding to 1 × 1015 molecules/cm2) a densely packed layer is reached. The work function increases by 1.31 eV. At θ=1/3 the adsorption energy decreases from its value of 26.5 kcal/mole by 3 kcal/mole. CO adsorption causes the appearance of two peaks at 6 and 14 eV in the electron energy loss spectra, which are ascribed to excitations of electrons from chemisorption levels. The sticking coefficient remains nearly constant up to medium coverages which can be described by a ``precursor'' state model. The results show close similarities with those reported for other nickelsurfaces.