Abstract
The influence of near-surface impurities on the enhanced sputtering of graphite near 600°C and above 1000° Chas been investigated under various doping conditions. The chemical sputtering yield of methane molecules for 2 keV D+ ions on graphite at 600°C has been determined for several coverages of Si, Fe, Ni, Ti, Mo, and Au. Graphite samples were pre-deposited with ~ 500 Å of a given impurity, and weight loss was monitored in-situ using a vacuum balance while sputtering through the deposited layer. Small amounts of impurities remaining on the surface after prolonged sputtering reduced chemical erosion by 30–50%. The radiation-enhanced sublimation of graphite observed for energetic ion bombardment above 1000°C was investigated during 50 keV Ar sputtering and simultaneous Ti evaporation. For very low surface concentrations of Ti, graphite sputtering increased while for concentrations above 10 at% the yields were significantly reduced. A graphite sample containing 4 at% bulk Si was also investigated and showed greatly reduced chemical erosion at 600° Cbut no reduction in radiation-enhanced sublimation at 1500°C due to surface enrichment and depletion of Si for the low- and high-temperature irradiation, respectively.
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