Sputtering of graphite with light ions at energies between 20 and 1000 eV

Abstract

Measurements of the physical and chemical sputtering yield of different sorts of graphite with H, D, and He ions have been extended down to energies of 20 eV. H + 3, D + 3, and He + ions of 3 keV have been decelerated in front of the target to energies of 60 eV. The target temperature could be varied between room temperature and 1000 K by simultaneous electron bombardment. The sputtering yield was obtained from the weight loss determined in situ using a vacuum balance, and the reaction products were analyzed using a liquid nitrogen-cooled quadrupole mass analyzer. At room temperature, the yield curve for He ions decreases at low energies as predicted by physical sputtering theory. For H + and D +, however, below 100 eV the sputtering yield increases with decreasing ion energy. It could be shown that this increase is due to the formation of CH 4 and CD 4, respectively. For ion energies of 500 eV and higher, chemical sputtering occurs only in a narrow temperature region between 700 and 900 K. This temperature region for chemical sputtering broadens at low ion energies and extends below 100 eV down to room temperature. Simultaneously, the maximum sputtering yield at 825 K decreases with decreasing energy and the temperature variation of the yield at energies below 100 eV is not very pronounced. For 50 eV, D + sputtering yield values vary between 2 × 10 −2 atoms/ion and 5 × 10 −2 atoms/ion between room temperature and 900 K.