Electron induced decomposition of Ni(CO) 4 adsorbed on Ag(111)

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 Ni x (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, Ni x (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 cm 2, and is not strongly dependent on incident electron energies between 100 and 300 eV.