Abstract
We present experimental methane production yields for H+, H2+, H3+, and D2+ ions incident on ATJ graphite in the energy range 10-250 eV/H. Below about 60 eV/H, the molecular H species give higher methane yields/H when compared with isovelocity H+, similar to our earlier measurements for incident deuterium atomic and molecular ions. For both D and H atomic and molecular projectiles, the yields/atom coalesce onto a single curve below projectile energies of ∼60 eV/atom, when plotted as a function of maximum energy transfer, under the assumption that, below this energy, the incident molecular species are largely undissociated when undergoing C-C bond breaking collisions during their collision cascade and thus produce more damage. Raman spectroscopy of a graphite sample exposed to high fluences of D+ and D3+ beams at high and low energies qualitatively confirmed the assumption that more surface damage is produced by the low-energy incident molecular species than by isovelocity atomic ions. While the two high-energy beam-exposed spots showed similar damage, the low-energy molecular-beam-exposed spot showed slightly more damage than the corresponding D+-beam-exposed spot.
Original language | English |
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Pages (from-to) | 880-887 |
Number of pages | 8 |
Journal | Vacuum |
Volume | 82 |
Issue number | 9 |
DOIs | |
State | Published - May 2 2008 |
Funding
This research was sponsored by the Office of Fusion Energy Sciences and the Office of Basic Energy Sciences of the US Department of Energy under Contract no. DE-AC05-00OR22725 with UT-Battelle, LLC. HZ was appointed through the ORNL Postdoctoral Research Associates Program administered jointly by the Oak Ridge Institute of Science and the Education and Oak Ridge National Laboratory.
Keywords
- Chemical sputtering
- Graphite
- Surface damage
- Surface modification