Surface defect production on Ge(001) during low-energy ion bombardment

Low-energy ion bombardment of the Ge(001)-(2×1) surface produces surface point defects, which are detected and quantified using in situ reflection high-energy electron diffraction. Surface defect production rates are determined for a range of ion energies and ion masses. At low substrate temperatures (T≊−100 °C), copious production of surface defects is observed, with defect yields as high as 20–30 defects per ion for 500 eV Ar and Xe bombardment. The observed He surface defect yields exceed the surface yield predicted by binary collision simulations, indicating that defects created in the subsurface region migrate to the surface for these conditions. The observed surface defect yield is reduced at elevated substrate temperatures. Based on a simple model this reduction is attributed to surface recombination of point defects created within the same cascade. A constant surface defect yield is reached at temperatures greater than 100 °C which is consistent with the net defect production due to the vacancies left by sputtering. However, even at elevated temperatures, significantly larger populations of mobile point defects than can be accounted for by sputtering may reside transiently on the surface, which can modify the overall surface morphology.