Surface defects created by 20Â keV Xe ion irradiation of Ge(1Â 1Â 1)

Surface defects created by 20 keV Xe ion irradiation of Ge(1 1 1) are investigated by scanning tunneling microscopy (STM). One bilayer deep vacancy islands and surface craters with a depth of more than two bilayers are observed. The creation of the surface craters, which is caused by thermal spike of 20 keV Xe ions, is an unusual event with a yield of ∼0.1%. The areal density of surface craters increases linearly with increasing ion fluence at 215 °C and increases sublinearly with increasing ion fluence at 275 °C.