Recoil implantation effects in ion impact desorption of monolayer adsorbates on solid surfaces

Abstract

Ion impact desorption of monolayer adsorbates on solid surfaces has been generally explained by three main terms: (I) reflection of direct knock-on adsorbate recoils, (II) knock-off by reflected projectiles and (III) knock-off by cascade collisions. In the case I, some fraction of the knock-on adsorbate recoils, not reflected, are implanted into the substrate. For evaluation of recoil-implantation effects on the adsorbate decay profile, mass balance equations for adsorbates at the top-surface and recoil-implanted in the sub-surface layers are proposed taking into account the desorption, recoil-implantation and collisional mixing with anisotropic effect. It is shown that the experimental decay profiles obtained by surface non-sensitive analysis techniques such as RBS are non-(bi-) exponential due to the recoil-implantation effect and that the analysis of the decay profiles provides the cross-sections for desorption and recoil-implantation. The recoil implantation cross-sections are compared with the theoretical recoil-production cross-sections. Finally, it is demonstrated that the recoil-implantation cross-section is used to characterize the well-defined ordered-adsorbates on monocrystalline surfaces, namely Si(111)√3 × √3-Au and -Ag surfaces.