Local triboelectricity on oxide surfaces

In triboelectric phenomena,, electric charges are transferred when two materials are touched or rubbed together. We present in this paper a study of this effect performed on metallic oxides at the nanometric scale by an Atomic Force Microscope in the resonant mode. We show that following the electrification processes, positive or negative charges can be deposited. From our experimental data, we conclude that the charge transfer results in an equilibrium final state, the occupied states in the gap being "surface states" with large density and spread under the surface along a characteristic distance of about 100 nm.