We measured the frictional behavior acting on C60 films at a small normal load as a function of oscillation amplitude using a MHz-range quartz crystal resonator and an optical AFM cantilever. The frictional behavior for C60 films varies by the amplitude: For the amplitudes smaller than the C-C bond length of the C60 molecule, the dynamic frictional force is directly proportional to the amplitude, while it becomes almost constant for larger amplitudes. Although the observation is in qualitatively the same manner as HOPG, the dynamic frictional force for small amplitudes is significantly larger than that of HOPG. This difference suggests that C60 molecules easily tilt and/or rotate when the tip slides in C60 films, and the dynamic friction arises from the tilting and/or rotating motion.

We carried out the surface mapping of the dynamic friction and the effective elastic stiffness of contact by using a quartz crystal resonator and an AFM cantilever, associated with the topographic image. The tip was scanned across the Au substrate on the resonator in the constant-height mode. A typical grain structure of the Au substrate in the dynamic friction and the effective stiffness images was observed, simultaneously with the topographical image. This technique enables us to observe the surface properties related to contact in the nanometer scale.