FORMATION AND HEALING OF DEFECTS AT THE SI(111)7X7 SURFACE UNDER LOW-ENERGY ION-BOMBARDMENT

We studied the formation and healing of adatom defects on a Si(111)7x7 surface bombarded by 0.5-keV Ar ions. Scanning tunneling microscopy s howed that adatoms were missing from the Si(111)7x7 surface. Increasin g the temperature during the bombardment increased the percentage of m issing adatom sites. However, the percentage saturated at 400 K, then decreased with temperature. This temperature dependence was due to com petition between the formation and healing of adatom defects; defect f ormation dominated at low temperatures, but was overcome by healing at high temperatures. We analyzed the temperature dependence using a rat e equation for missing adatoms which included the temperature-independ ent sputtering and other temperature-dependent formation and healing p rocesses. Activation energies of 0.29 and 0.39 eV were obtained for th e temperature-dependent formation and the healing of adatom defects. T he temperature-dependent formation was attributed to vacancy-adatom re combination, and the temperature-dependent healing was attributed to t he interstitial atom-missing adatom site recombination. These vacancy and interstitial atoms were generated in the collision cascade under t he surface. Some of them migrated to the surface and contributed to th e temperature-dependent formation and healing of missing adatoms.