ENERGY-TRANSFER AND SURFACE-INDUCED DISSOCIATION FOR SIME3+ SCATTERING OFF CLEAN AND ADSORBATE COVERED METALS

We scatter 10-70 eV SiMe3+ from clean Au(111), a hexanethiolate self-a ssembled monolayer on Au(111) (C-6), and a NiO(111) layer grown on top of Ni(111). We examine both the scattered ion fragmentation patterns and the kinetic energy distribution spectra (KEDS) as a function of th e incident ion energy E. Surface infrared and KEDS data indicate that we have prepared a saturated monolayer of hexanethiolate (C-6) on Au(1 11) where the C-6 carbon backbone is predominantly upright on the surf ace. C-6 monolayers with a mixture of prone and upright C-6 can also b e prepared, but only the upright C-6 monolayers are used for ion scatt ering experiments. The fragment ion distributions and the KEDS are the n used to determine the channeling of the incident SiMe3+ ion energy i nto the scattered ion internal energy E-int, and the scattered ion kin etic energy E-scat. Overall, we find the order of E-int/E for SiMe3+ t o be Au(111)much greater than NiO(111)>C-6. From the E-scat values, we find that MiSe(3)(+) scattering off C-6 is highly inelastic while sca ttering off Au is much more elastic. We use this information to calcul ate the energy (E-surf) which is channeled into the surface as a resul t of the collision for C-6 and Au(111). By comparing the KEDS for the parent and fragment ions, we determine the importance of unimolecular dissociation off the various surfaces. In the accompanying paper, we p resent a series of classical dynamics simulations to explain and suppl ement these experimental results. (C) 1997 American Institute of Physi cs.