Energetic D⁺ and He⁺ impinging on solid beryllium: Observation of physical and chemically assisted atomic and molecular ion sputtering

Our Surface-Time-Of-Flight (SurfTOF) tandem mass spectrometer apparatus has been employed in a comparative investigation of ion sputtering induced by mono-energetic D+ and He+ ion beams impinging on a Be surface at 700 K with impact energies from 5 to 500 eV. Both chemically assisted sputtering (by D+ impact below 50 eV) and physical sputtering (by He+ and D+ above 50 eV) were observed. Be+ was the dominant sputtered ion at all energies. Chemically assisted sputtering mechanisms are proposed for the concomitant chemical sputtering of Be+, Be-2(+) and BeD+ ions (by D+ at low energies). Evidence was also obtained for the sputtering of BeO+ and Be2O+ by both He+ and D+ impact ions (with a minimum at 30 eV with D+), but only above 30 eV with He+. They are ascribed to the presence of BeO and Be2O impurities in the surface layer of Be. Water molecules adsorbed on the Be sample gave rise to BeH+ and BeOH+ in the sputtered ion spectrum primarily at higher energies above 30 eV where Be+ ejection is enhanced. Combined observations with a quartz crystal microbalance and a Faraday cup provided preliminary insight into the sputter yields of neutral and ionized beryllium. These results can be carried over to the erosion of Be by plasma deuterons, and T+ by extension, in its use as the first wall for the ITER blanket in fusion technology.