D and D/He plasma interactions with diamond: Surface modification and D retention

Abstract

Chemical vapour deposition (CVD) diamond is of interest as a plasma facing material in magnetically confined nuclear fusion devices. CVD diamond samples were exposed to ion fluences between 1.5×1022ionsm−2 and 1×1024ionsm−2 in D, D/He and He plasmas. A significant surface coverage of 10nm–100nm sized hemispherical and conical surface features resulted from chemical erosion and subsequent redeposition on samples exposed to≥1023ionsm−2 when exposed to D containing plasmas. Near edge X-ray absorption fine structure (NEXAFS) spectra showed strong diamond features following plasma exposure, indicating that the diamond crystal structure on the surface was largely retained. A small increase in the sp2 fraction (from 1.2% to 4–7%), was observed suggesting some amorphous carbon formation. Elastic recoil detection analysis (ERDA) revealed that D retention saturates at ~5.4% averaged over the depth resolution of 20nm from the surface, for an ion fluence of ~1023ionsm−2. The addition of He to the plasma resulted in a slower uptake of D, which was attributed to He ion induced desorption of D.