Force-microscopy measurements are performed on the Si(111) surface. The 7×7 reconstruction is observed in the repulsive contact mode. With applied contact pressures of 1–10 GPa the reconstructed surface remains stable. Variations of frictional forces of the order of ${10}^{\mathrm{-}9}$ N are observed on the atomic scale.

• Received 1 November 1994

DOI:https://doi.org/10.1103/PhysRevB.51.5484