Interatomic Forces in Scanning Tunneling Microscopy: Giant Corrugations of the Graphite Surface

We show that scanning tunneling microscopy (STM) images can be dominated by elastic deformations induced by atomic forces between tip and surface. New STM experiments on graphite (0001) showing a strong variation of the giant corrugation amplitudes with varying current at constant voltage are direct evidence of this atomic-force concept. Corrugations up to 8 A on a lateral scale of 2. 4 are associated with forces up to 10^-8 N for compression and 2 10^-10 N for expansion.