Radiation-Enhanced Sublimation of Graphite Materials due to Hydrogen Ions

Abstract

For isotropic graphite, C/C composite and pyrolytic graphite, yields of Radiation-Enhanced Sublimation (RES) due to hydrogen ion bombardment were measured in the temperature range up to 2000K by weight loss method. Graphite samples were irradiated by H3+ ions with the energy of 4.5keV and fluences from 1019H/cm2 to 1020H/cm2. The RES yields measured showed no clear differences among these three types of isotropic graphite and the pyrolytic carbon. Namely, the RES did not depend on physical properties and/or structure of graphite. The activation energy corresponding to the RES was approximately 0.8eV for the isotropic graphites. The angular dependences of sputtering at various temperature were also examined. The result showed that the physical sputtering yield increased with ion-incident angle, but the chemical sputtering and RES yields were approximately independent of the incident angle.Raman spectra of the samples as-received and irradiated in RES regime were examined. While R-number (=I1360/I1585) before irradiation varied with the kind of graphite samples, the value became almost the same for every graphite sample irradiated at elevated temperature. In the RES regime, the sample irradiated at higher temperature showed better crystallinity than that at lower temperature. The change of surface morphology due to irradiation was also examined by Scanning Electron Microscopy.