ION-BEAM MIXING OF ISOTOPIC SILVER BILAYERS BY 200 KEV GERMANIUM

Bilayers of 20 nm Ag-107/55 nm Ag-109 grown on Si(100) were implanted at 300 K with 3, 6 and 9 x 10(15) cm-2 200 keV Ge-72. The implantation caused sputtering of the film and intermixing at the interface. The sputter rate found from RBS analysis of the films was consistent with TRIM89 estimates. SIMS depth profiling using 2 keV O2+ showed that the standard deviation of an error function fit to the depth profile across the interface increased from 8 to 29.7 nm with increasing Ge dose. This is consistent with a mixing efficiency of 210+/-40 angstrom5 eV-1. This value is of the same magnitude as that predicted by the thermal spike theory of Koponen and Hautala. Using the scaling procedures in that theory the present result also agrees with 10 keV Xe+ room temperature mixing of isotopic silver films and 330 keV Kr+ mixing of impurities in Ag at 77 K.