Deformation of the contact region and adhesional friction between nanoprobe and surface

The problem is studied (theoretically) of the characterization of the equilibrium shape and atomic structure of loaded nanotribocontact between a rigid paraboloidal tip of an atomic force microscope and a soft surface that is modelled by a sequence of parallel atomic planes. The structural, energy and force characteristics are calculated of dissipative (velocity-independent) adhesional friction force versus normal force and tip radius of curvature in the system of diamond (tip)–graphite (surface). Several approximations to the interatomic potentials are used. It is shown that interface deformation leads to a decrease of the friction force under tensile (negative) stress. For positive loading forces in the range of 0–80 nN, the change in friction depends on the tipʹs radius of curvature and the type of interatomic potential used. An approximate proportionality between the friction force and the tip radius is obtained. A comparison of the theoretical results with experimental data in ultrahigh vacuum is given.