Superlubricity in two-dimensional contacts of elastic solids with rough surfaces

The recently developed Green's-function molecular-dynamics technique is used to study the possibility for superlubricity in two dimensions. Elastic solid bodies in contact with rough surfaces are considered within the current approach. Surface topographies were either acquired from the results of atomic force microscopy experiments or created using a self-affine fractal generator algorithm. Interactions between the solids are modeled via hard-wall or exponentially repulsive potentials. Our results show evidence of a superlubric state whenever the hard-wall approximation is considered. In the case of exponential walls, the static friction coefficient on ideal surfaces appears to be only a function of the mean-square slope of the height profiles. Additionally, for experimental topographies, variations in the roughness of the very last layer prove to play a key role in achieving ultralow friction.