Self-recovery of monolayer Pb adsorbates on the Si(111)-1×1-Pb surface under ion irradiation at room temperature

Abstract

The concentration change of Pb at the Si(111)-1×1-Pb surface by 5keV Ar+-ion bombardment has been measured by means of XPS and RBS techniques in order to determine the cross-sections for desorption and recoil-implantation of Pb adsorbate. It is found that the normalized concentration of Pb by XPS decreases exponentially with increasing Ar+-ion fluence, while that by RBS decreases exponentially to 0.2 and eventually reaches a constant level of ∼0.1. We have evaluated the potential barrier heights for desorption and recoil-implantation to be 1.8±0.1eV and 90±40eV, respectively, from the obtained cross-sections. It is concluded that the extremely large value of the potential barrier height for recoil-implantation indicates that most of the Pb atoms which have been recoil-implanted by the Ar+-ion into subsurface layers from the Si(111)-1×1-Pb surface segregate back rapidly to the original surface even at room temperature before the original surface is again bombarded by the next ion, which is called self-organization when the original structure is reformed locally.