Oxidation effect on the shear strength of graphene on aluminum and titanium surfaces

We report the interfacial shear strength of graphene on pure and oxidized Ti and Al metal surfaces using density functional theory calculations. Our results show significant changes to the graphene-metal bonding properties in the presence of an oxide phase. In particular, the strongly chemisorbed interface between graphene and pure Ti is drastically weakened by the formation of a metal-oxide phase, while the weakly physisorbed interface between graphene and pure Al is significantly strengthened through the metal oxide formation. These oxidation effects can be modulated to some extent by the presence of vacancy or Stone-Wales defects which increases the binding interactions of weaker graphene-metal interfaces. These dramatic changes to the interfacial properties by surface oxidation explain the results of recent carbon nanotube pull-out experiments from Al and Ti metal-matrix nanocomposites.