Chemical sputtering of room temperature ATJ graphite and HOPG by slow atomic and molecular D ions

We present experimental results for methane production from ATJ graphite and highly oriented pyrolytic graphite (HOPG) produced by atomic and molecular D ions in the energy range 5–150 eV/D. For the ATJ graphite target, a systematic trend of the methane yields for the different molecular species compared at the same impact energy/D is observed. While all three species lead to methane yields that coincide within the experimental uncertainty at the high energy end of the investigated range, at lower energies the yields diverge progressively; the incident triatomic molecular ion leads to the largest yields per atom, and the atomic ion to the smallest. The difference at the lowest investigated energy (10 eV/D) is about a factor of two. The measured yields were found to be in good agreement with recent in house molecular dynamics simulations. Results are presented for two different HOPG basal plane orientations relative to the surface plane, one parallel, the other perpendicular. Differences in the methane yields for the two orientations are observed at the higher investigated energies that suggest reduced diffusion from the sample bulk when the basal planes are oriented parallel to the surface plane. A similar reduction is not observed in case of acetylene production, suggesting that the acetylene is produced mainly at the target surface.