Comparing hyperthermal molecular and atomic ion sputtering of adsorbates:: Xe+ versus SF5+ on NH3/CO/Ni(111)

Polyatomic ion-induced desorption of adsorbates is an important effect in secondary ion mass spectrometry, surface-induced dissociation and both ion beam and plasma processing of materials. We compared the adsorbate desorption cross-sections for a model ion-adsorbate system, NH3/CO/Ni(111) exposed to the isobaric atomic and polyatomic ions, Xe+ and SF5+, with kinetic energies of 10-1000 eV. The depletion of the adsorbate layer and the formation of new surface chemical species were monitored by X-ray photoelectron spectroscopy. Two to three times higher desorption cross-sections for both NH3 and CO were observed for SF5+ ion bombardment compared with Xe+ at the same incident energy. TRIDYN Monte Carlo simulations generally gave good agreement with the experimental results. TRIDYN implicated the larger reflected ion contributions for S and F compared with Xe as the source of the enhanced desorption yields by the polyatomic ion. Substrate damage was also found to be lower for SF5+ than Xe+ due to the former's lower energy per atom and lighter constituent atom masses. (C) 1998 Elsevier Science B.V.