Dynamical frictional force of nanoscale sliding

We measured the dynamical frictional force acting on highly oriented pyrolytic graphite and C-60 substrates by a sliding Si3N4 tip as a function of sliding distance using the probe-tip-quartz-crystal-resonator technique. It was found that the dynamical frictional force undergoes a drastic change when the oscillation amplitude is approximately the lattice constant of each substrate: For a small case, it is directly proportional to the amplitude, while for a large case, it does not depend on the amplitude. The observed behavior is qualitatively understood by a simple one-dimensional Tomlinson model.