SIMULATION OF ENERGY-DEPENDENT ISOTOPE SPUTTERING

The flux of atoms sputtered from an isotopic mixture is known to be en riched in the light component(s). Measured enrichment factors have bee n reported that significantly exceed those predicted by high-energy sp utter theory. Moreover, a dependence on the emission angle is observed which was not predicted either but had been found in numerical simula tions. To resolve this puzzle, we have simulated the sputtering of iso topic mixtures for ion energies ranging from 100 eV to 100 keV and fou nd the isotopic enrichment to be very sensitive to the energy of the b ombarding ion beam. Our computed enrichment factors are consistent wit h values measured at low beam energies. They also reach an asymptotic value in agreement with the theoretical high-energy prediction. Simila rly, a pronounced angular dependence is found at low beam energies whi ch becomes much smaller in the high-energy limit.