Rapid back-segregation effects on recoil implantation of monolayer Pb adsorbates at Si(1 1 1) surfaces by keV Ar ion impact

The decay curves of Pb coverage at the Si(1 1 1)-1x1-Pb surface by 5 keV Ar+ ion impact have been measured, by means of the Rutherford backscattering (RBS) technique, with successive irradiation for the short period at low ion fluxes at temperatures of 300 K and 200 K and with a continuous irradiation for the long period of 600 s at different ion fluxes at 300 K. For the successive short period irradiation it is found that the decay curves of Pb coverage measured under different conditions correspond with each other and with the previous one. The result is reasonably explained in terms of complete recovery (back-segregation) of Pb adsorbates recoil-implanted once by one Ar+ ion impact before the next Ar+ ion impacts on the same local position. For the continuous long period irradiation at high ion fluxes it is found that the decay fractions of Pb coverage increase with increasing the ion flux. The result is also reasonably and quantitatively explained in terms of back-segregation and additional radiation-induced segregation of recoil-implanted Pb adsorbates