Energy transfer and surface-induced dissociation for SiMe3+ scattering off clean and adsorbate covered metals

Abstract

We scatter 10–70 eV SiMe3+ from clean Au(111), a hexanethiolate self-assembled monolayer on Au(111) (C6), 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 the incident ion energy E. Surface infrared and KEDS data indicate that we have prepared a saturated monolayer of hexanethiolate (C6) on Au(111) where the C6 carbon backbone is predominantly upright on the surface. C6 monolayers with a mixture of prone and upright C6 can also be prepared, but only the upright C6 monolayers are used for ion scattering experiments. The fragment ion distributions and the KEDS are then used to determine the channeling of the incident SiMe3+ion energy into the scattered ion internal energy Eint, and the scattered ion kinetic energy Escat. Overall, we find the order of Eint/E for SiMe3+ to be Au(111)≫NiO(111)>C6. From the Escat values, we find that MiSe3+ scattering off C6 is highly inelastic while scattering off Au is much more elastic. We use this information to calculate the energy (Esurf) which is channeled into the surface as a result of the collision for C6 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 present a series of classical dynamics simulations to explain and supplement these experimental results.