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Abstract: We have experimentally determined total carbon yields per incident H atom in the energy range 36–300eV/H for H+, , and projectiles incident normally on ∼60nm thick a-C:H films, using 2-D ellipsometry determination of erosion crater volumes ex vacuo, the separately characterized thin film carbon density, and the incident beam current integration accumulated on target during the crater evolution. During each beam exposure, methane production was monitored using in situ quadrupole mass spectrometry (QMS). The present total carbon yields/H for incident ions obtained via ellipsometry are in agreement with total mass loss measurements for by Balden and Roth over the investigated energy range. The observed methane production per incident H for the molecular ions exhibits molecular size effects over the entire energy range investigated, confirming the trend observed in the ellipsometry-based total C yields/H. [Copyright &y& Elsevier]

Abstract: We report measurements of total C sputtering yields for room temperature a-C:D thin films irrradiated by equal velocity D+, , and beams in the energy range 30–200eV/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 ions are in good agreement with mass loss measurements for , our results for and D+ incident ions fall systematically below the 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+, , and 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. [Copyright &y& Elsevier]