On the preferential emission of heavy isotopes in sputtering

Abstract

The isotopic composition of secondary ions of boron were measured at a small emission angle by bombarding boron nitride with xenon ions at energies ranging from 100 eV to 1.5 keV. An ion gun was used to generate the ion beam. The secondary ions were detected by a quadrupole mass spectrometer. A flood electron gun was used to neutralize the positive charge build-up on the target surface. The secondary-ion flux was found to be enriched in heavy isotopes at lower incident ion energies. The heavy isotope enrichment was observed to decrease with increasing primary-ion energy. Beyond 350 eV, light isotopes were sputtered preferentially with the enrichment increasing to an asymptotic value of 1.27 at 1.5 keV. This trend is similar to that of the isotopic enrichment observed earlier when copper was sputtered with xenon ions in the same energy range.