Erosion of a-C:D thin films by low energy D+, D2+, and D3+ ion beam irradiation

We report measurements of total C sputtering yields for room temperature a-C:D thin films irrradiated by equal velocity D+, D2+, and D3+ beams in the energy range 30-200 eV/D. The C sputtering yields were deduced from crater volumes determined from 2-D ellipsometry scans, the known thin film C density, and the measured total number of incident D particles during the beam exposures. While our results for incident D3+ ions are in good agreement with mass loss measurements for D3+, our results for D2+ and D+ incident ions fall systematically below the D3+ results, indicating a significant molecular size effect. A molecular size effect has been previously found for CD4 production during low energy impact of same velocity D+, D2+, and D3+ ions incident on ATJ graphite, which, however, was smaller in magnitude. The ellipsometry-based total C sputtering yields are compared with recently deduced total C production yields based on a mass spectroscopy approach.