Atomic force microscopic measurements were carried out on the (111) surface. The 7 x 7 reconstruction was observed in the repulsive contact mode. Under applied contact pressures of 1 to 10GPa, the reconstructed surface remained stable. Variations in frictional force which were of the order of 10-9N were observed at the atomic scale.

L.Howald, R.Lüthi, E.Meyer, H.J.Güntherodt: Physical Review B, 1995, 51[8], 5484-7