A simple model for the lowest excited states of α-CO/W (100): application to electron stimulated desorption: J Rubio et al,Vacuum, 32, (12). 1982, 719–722.

Abstract

Nickel tetracarbonyl (Ni(CO)4) adsorption on Ag(111) was studied with temperature-programmed desorption (TPD), digital electron-stimulated desorption ion angular distribution (ESDIAD) and Auger electron spectroscopy (AES). Ni(CO)4 physisorbs molecularly at 90 K on Ag(111), with thermal desorption maxima observed near 170 and 150 K. Analysis of AES spectra indicates no Ni, C or O is present at the surface following TPD, showing that Ni(CO)4 does not thermally decompose on Ag(111). Bombardment by 100–300 eV electrons induces positive ion and excited neutral particle desorption, and conversion of molecularly adsorbed Ni(CO)4 into unidentified Nix(CO)y surface species. CO thermally desorbs from these surface-bound species near 240, 300 and 400 K, leaving a Ni deposit on the Ag surface. This Ni diffuses below the surface above 450 K. ESDIAD patterns from molecularly adsorbed Ni(CO)4 are composed of ESD fragments (CO+, O+, and neutrals) ejected normal to the surface, suggesting that Ni(CO)4 on Ag(111) orients one CO ligand nearly perpendicular to the substrate. In contrast, Nix(CO)y surface species do not produce directed ESDIAD beams, possibly reflecting a non-normal or random orientation of CO ligands in these adspecies. The total cross section for electron induced Ni(CO)4 fragmentation is about 2 × 10−16 cm2, and is not strongly dependent on incident electron energies between 100 and 300 eV.