Analysis of experimental load dependence of two-dimensional atomic-scale friction

By using a two-dimensional frictional force microscope, we experimentally investigated and analyzed load dependence of atomic-scale friction between a single asperity tip and an atomically flat surface of graphite. While the tip shows the two-dimensional discrete jump between the sticking domains with the lattice periodicity in the higher load region, in the lower load region the tip shows rather smooth motion. The extent of the sticking domain decreases by increasing the load. Further, the appearance frequency of the zigzag motion of the discrete jump decreases by increasing the load. These results are explained by the load dependence of the effective adhesive region.