Intercalation of two-dimensional graphite films on metals by atoms and molecules

Abstract

An analysis is made of some general laws governing a new physical effect, i.e., the spontaneous penetration of particles (atoms, C60 molecules) adsorbed on a two-dimensional graphite film on a metal (Ir, Re, Pt, Mo,...) to beneath the graphite film (intercalation). It is shown that atoms having low ionization potentials (Cs, K, Na) intercalate a two-dimensional graphite film on iridium at T=300–400K with an efficiency χ≈0.5, accumulating beneath the film to a concentration of up to a monolayer. Atoms having high ionization potentials (Si, Pt, Ni, C, Mo, etc.) intercalate a two-dimensional graphite film on iridium at T≈1000K with an efficiency, χ≈1, forming beneath the film a thick intercalate layer which is strongly bonded chemically to the metal substrate but is probably weakly bonded to the graphite monolayer by van der Waals forces. The presence of a graphite “lid” impeding the escape of atoms from the intercalated state up to record high temperatures T∼2000K leads to superefficient diffusion (with an efficiency close to one) of various atoms (Cs, K) into the bulk of the substrate (Re, Ir).