Dramatic reduction of chemical sputtering of graphite under intercalation of lithium

Abstract In previous studies, in situ deposition of a lithium thin layer onto graphite was found to considerably suppress physical sputtering of graphite, owing to rapid diffusion of Li into graphite bulk (so-called intercalation). This paper reports that the Li intercalation dramatically reduces graphite chemical sputtering as well, once the Li-deposited surface is cleaned by hydrogen plasma. This is evidenced in a small-scale plasma experiment on the Li-deposited graphite in hydrogen glow, comparing with an ultra-high-vacuum beam experiment. In the latter experiment, energy-controlled H2+ beam is irradiated on a Li-deposited graphite sample where methane yield is measured together with in situ surface analysis of graphite by X-ray photoelectron spectroscopy. Both the plasma experiment and the beam experiment showed similar temporal variations of methane yield after the hydrogen exposure of the Li-deposited graphite. Namely, the methane yield gradually decreases down to a negligible level compared with the pure graphite case. The XPS analysis of surface atoms (O, C, Li) suggests that the hydrogen plasma exposure gives rise to removal of Li-containing impurities on the graphite surface. As a consequence, the hydrogen glow conditioning results in an almost complete suppression of chemical erosion of graphite below 500 K.