Tribological behavior of a charged atomic force microscope tip on graphene oxide films

The tribological behavior of graphene oxide (GO) films deposited on a mica substrate has been investigated by atomic force microscopy, in which different voltages were applied to a tip. It was found that the frictional forces on the GO films remain unchanged in the presence of negative tip voltages, while the frictional forces increase remarkably with an increase of the voltage when positive voltages are given to the tip, and at a certain positive tip voltage the frictional forces reach a stable value with increasing number of repeated cycles. To study the influence of the tip voltage on the frictional forces of the GO films, the adhesive and electrostatic force gradients between the tip and GO films were measured. The results showed that the adhesive and electrostatic forces increased with increase of the positive tip voltages. This phenomenon is due to the polarization of charges in the GO films induced by the applied tip voltages, which causes intensive electrostatic interactions between the tip and GO films and a corresponding rise in the adhesive forces and the frictional forces.