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 adso rbate 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 adsor bate layer and the formation of new surface chemical species were moni tored by X-ray photoelectron spectroscopy. Two to three times higher d esorption cross-sections for both NH3 and CO were observed for SF5+ io n bombardment compared with Xe+ at the same incident energy. TRIDYN Mo nte Carlo simulations generally gave good agreement with the experimen tal 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 lo wer for SF5+ than Xe+ due to the former's lower energy per atom and li ghter constituent atom masses. (C) 1998 Elsevier Science B.V.