Localized Fluctuation of a Two-Dimensional Atomic-Scale Friction

By carrying out a fast line scan 10° tilted from perpendicular to a row of the stick-points on a cleaved graphite surface, we observed localized fluctuation of a two-dimensional atomic-scale friction using a two-dimensional frictional force microscope. The analysis which was based on a two-dimensional stick-slip model revealed that the localized fluctuation on an atomic scale exhibits three kinds of tip trajectory and that one trajectory exhibits a slip motion with an almost 90° angle from the fast line scan direction. This localized fluctuation enabled us to observe square-wave signal with a subangstrom lateral width which indicates the achievement of subangstrom lateral resolution with a microscope for the first time. Furthermore, the origin of the three possible trajectories was explained well by an extended two-dimensional stick-slip model with the effective adhesive area. Therefore, this extended model is useful for studying the origin of the fluctuation of an atomic-scale friction.