Friction force microscopy experiments in ultrahigh vacuum allow the observation of atomic-scale stick-slip processes on Cu(111) surfaces. The lateral stiffness of the contact and the electrical characteristic of the junction are discussed. It is suggested that the tip is covered by copper forming a contact of a few atoms with the Cu(111) surface. The mean friction exhibits a clear dependence on the scan velocity.

• Received 8 July 1999

DOI:https://doi.org/10.1103/PhysRevB.60.R11301