Erosion Processes of Carbon Materials under Hydrogen Bombardment and their Mitigation by Doping

Two regimes of the chemical erosion of carbon materials under hydrogen bombardment have been separated: (i) the thermally activated regime, Y_therm, with the maximal erosion yield in the temperature range between 550 and 850 K, and (ii) the so-called "surface" regime, Y_surf, at low temperatures (~300 K) and low impact energies (< 100 eV). Doping carbon materials largely reduces their chemical reactivity with hydrogen and their chemical erosion. In addition, dopant enrichment at the surface due to preferential sputtering of carbon contributes to a reduction of the erosion yield. Erosion measurements with 30 eV and 1 keV D for various doped carbon materials with dopant concentration between 0.25 and 13 at.% were performed at temperatures between 77 and 1100 K. For Y_surf at high ion fluences (> 10²⁵ D/m²), a reduction of the erosion yield by one order of magnitude is observed for fine-grain carbide-doped graphites. Scanning electron microscopy (SEM) allows to associate these fluence dependencies with the evolution of a rough surface morphology of several µm in the erosion area. For Y_therm an almost complete suppression of the CD₄-production yield is observed for Ti-doped C layers. This reduction due to the doping on atomic scale exceeds all previously observed reductions of materials with a coarser dopant distribution. For all investigated carbon materials, the yield below RT does not depend on temperature.