Sticking of hydrocarbon radicals on different amorphous hydrogenated carbon surfaces: a molecular dynamics study.

In this study we investigate how the hydrogen flux administered to amorphous hydrogenated carbon (a-C : H) samples influences the sticking probability of hydrocarbon radicals on these samples. We bombard a-C : H samples that were previously subjected to different hydrogen fluxes with hydrocarbon radicals. The energy of the radicals is 10 eV. The sample temperatures are 700 and 1000 K. The results show that the sticking probability is larger on samples pre-irradiated with a higher hydrogen flux caused by the higher sp(2) fraction in the sample. This suggests that redeposition can contribute to the observed flux dependency of the carbon erosion yield.

Molecular dynamics simulations of amorphous hydrogenated carbon under high hydrogen fluxes.

We study the flux dependence of the carbon erosion yield and the hydrogen enrichment of the surface in the high flux regime at 10(28) ions per m(2) s and higher by using molecular dynamics (MD). We simulate an amorphous hydrogenated carbon sample exposed to high flux hydrogen bombardment with a hydrogen energy of 10 eV at surface temperatures of 700 and 1000 K. As interaction potential the reactive empirical bond order potential of Brenner-Beardmore is taken and energy dissipation is simulated with the Berendsen thermostat. The simulation results show that the carbon erosion yield is higher for higher sample temperatures but does not show a strong dependence on the hydrogen flux. Hence, the hydrogen enrichment in the upper surface layer observed in the simulations most likely does not contribute to the erosion yield reduction in the experiments. Furthermore, the composition of the eroded material shows a slight increase in CH, C(2)H and C(2)H(2) for higher fluxes, whereas species with more hydrogen, C atoms and C(2) are decreased. However, the H : C ratio in the eroded material shows no flux dependence.