Comparative study on friction force pattern anisotropy of graphite

In this paper, the experimental and theoretical studies on the atomic-scale two-dimensional friction force pattern are presented. Atomic-scale friction experiments were conducted on graphite surfaces with the atomic force microscopy (AFM) under ambient conditions. Owing to the dimensionality reduction effect of optical method detecting the probe cantilever deflection, the friction force patterns were revealed in these experiments. The friction phenomenon was analyzed theoretically in the framework of Prandtl-Tomlinson model in two dimensions. The dimensionality reduction effect was formulated and involved in the model. The comparison shows the good quantitative agreement between experimental and simulation results, suggesting that the friction force pattern can be interpreted reliably using the model. Meanwhile atomic arrangement was obtained in friction force pattern, the origin and variation of which were also analyzed. The condition for appearance of atomic arrangement was determined qualitatively. By means of band-pass filtering, hexagonal rings or crystal lattices images of graphite were obtained.