Self-organization of monolayer (Pb, Sn) adsorbates at Si(111) surface recoil-implanted by keV ion impact

Abstract

The concentration changes of Pb and Sn at the Si(111)- 7 × 3 -(Pb, Sn) surface by 5 keV Ar + ion bombardment have been studied by means of XPS, AES and RBS techniques with LEED and STM techniques, in order to determine their cross-sections for desorption and recoil-implantation of them. The potential barrier heights for desorption and recoil-implantation of Pb at the Si(111)- 7 × 3 -(Pb, Sn) surface have been determined to be 1.4 ± 0.2 and 200 ± 140 eV, respectively, from the obtained cross-sections, while those of Sn to be 3.2 ± 0.7 and 4.7 ± 2.8 eV, respectively. These data are found to be very similar to those for Si(111)-1×1-Pb and Si(111)- 2 3 ×2 3 + 3 × 3 -Sn surfaces. The extremely high potential barrier heights for recoil-implantaiton of Pb are explained in terms of self-recovery of Pb atoms, which have been once recoil-implantated into the subsurface layers by the Ar + ion, to the original surface before the next Ar + ion comes again to the original surface. Co-existence of Sn atoms at the Si(111)- 7 × 3 -(Pb, Sn) surface is shown to shorten the characteristic time for the self-recovery of Pb, which is concluded to give an evidence for the self-organization.