  Manipulation of metal nanoparticles using atomic force microscope is a
promising new technique for probing tribological properties at the nanoscale.
In spite of some advancements in experimental investigations, there is no
unambiguous theoretical treatment of processes accompanying the movement of
metallic nanoislands adsorbed on a flat surface and additional research is
required. In this paper, we describe computer experiments based on classical
molecular dynamics in which the behavior of silver and nickel nanoparticles
interacting with a graphene sheet and sheared with constant force is studied.
Frictional force acting on the nanoislands is measured as a function of their
size. It is shown that its average value grows approximately linearly with
contact area, and slopes of linear fits are close to the experimentally
observable ones. The dependence of the friction force value and of the shape of
the measured friction curves on the type of metal atom is revealed and its
possible reasons originating from atomistic background are discussed.
