Penetration of alkali atoms throughout graphene membrane: theoretical modeling

Theoretical studies of penetration of various alkali atoms (Li, Na, Rb, Cs) throughout graphene membrane grown on silicon carbide substrate are reported and compared with recent experimental results. Results of first principles modeling demonstrate rather low (about 0.8 eV) energy barrier for the formation of temporary defects in carbon layer required for the penetration of Li at high concentration of adatoms, higher (about 2 eV) barrier for Na, and barriers above 4 eV for Rb and Cs. Experiments prove migration of lithium adatoms from graphene surface to the buffer layer and SiC substrate at room temperature, sodium at 100{\deg}C and impenetrability of graphene membrane for Rb and Cs. Differences between epitaxial and free standing graphene for the penetration of alkali ions are also discussed.