  To determine the friction coefficient of graphene, micro-scale scratch tests
are conducted on exfoliated and epitaxial graphene at ambient conditions. The
experimental results show that the monolayer, bilayer, and trilayer graphene
all yield friction coefficients of approximately 0.03. The friction coefficient
of pristine graphene is less than that of disordered graphene, which is treated
by oxygen plasma. Ramping force scratch tests are performed on graphene with
various numbers of layers to determine the normal load required for the probe
to penetrate graphene. A very low friction coefficient and also its high
pressure resistance make graphene a promising material for antiwear coatings.
