Study of nanotribological properties of multilayer graphene by calibrated atomic force microscopy.

The nanotribological properties of multilayer graphene oxide (MGO), multilayer reduced graphene oxide (MRGO), and mechanically exfoliated multilayer graphene (MEMG) deposited on SiO(2) substrate were comparatively investigated via calibrated atomic force microscopy in ambient conditions. Friction as a function of the applied normal load and sliding velocity was studied. Results show that all three types of multilayer graphene films exhibit good adhesion and friction reduction properties. MEMG exhibits the lowest friction and adhesive force because of its perfect planar lattice. A logarithmic increase in friction was observed at low sliding velocities for all measured graphene films. Friction decreases on MGO and bare SiO(2) substrate, whereas it remains approximately constant on MEMG and MRGO, when the sliding velocity exceeds their critical velocities. The possible mechanisms for the experimental results were discussed. Our studies provide a good opportunity to use different types of multilayer graphene films for promising lubricant applications in nanodevices.