Defect formation in Si(111)7×7 surfaces due to 200 eV Ar⁺ ion bombardment

Surface x-ray diffraction measurements have been made to study defect formation at the atomic level in the near surface region of Si(111)7×7 surface during low energy (200 eV) Ar⁺ ion bombardment. We have observed the two characteristics of the defects: missing atoms at different layers in the surface region as well as outward strain. We provide calculations that demonstrate how crystal truncation rod (CTR) measurements are sensitive to these modifications in the surface regions. We find that the measurement is sensitive to lattice strain and site occupancy of individual atomic layers near to the surface. We have thus determined occupancy profiles that represent the density of missing atoms with depth after irradiation. Both the strain and the atom deficit are found to increase with dose while the two distributions extend to about the same depth. These results are consistent with simulations of the ion-solid interaction mechanism using SRIM2000 with appropriate choice of surface and bulk displacement energies.