Behavior of Li on graphene surfaces observed using high-resolution ERDA

Behavior of Li atoms deposited on the surfaces of highly oriented pyrolytic graphite (HOPG) and graphene-based thin films were observed at room temperature using high-resolution elastic recoil detection analysis (ERDA). On the HOPG surface, the deposited Li atoms intercalate into the bulk and no Li was observed in the surface region. The Li atoms were found to stay in the surface region (from the surface down to at least 3 nm) when the HOPG was irradiated with 200 keV He ions to a fluence of 5 × 1015 ions/cm2 before Li deposition. This indicates that stable Li sites are produced by the ion irradiation. It was also found that Li atoms are accumulated on the surface due to the oxidation by the residual gas. This oxidation occurs only on the surface and not inside HOPG. Graphene-based thin films were prepared on Cu by microwave plasma chemical vapor deposition. The Li atoms deposited on the graphene-based thin films are found to distribute through the film almost uniformly and no accumulation either on the surface or at the interface was observed.