Frictional Force between a Sharp Asperity and a Surface Step

Abstract

We report a detailed study of the frictional force between the tip of a scanning force microscope and a step on a crystalline surface. Experiments on surfaces of freshly cleaved graphite reveal different contributions to the lateral force at steps with distinctly different dependencies on normal load and scan direction. The different contributions can be attributed to topography-induced tip twisting and an increased dissipative force due to the Schwoebel barrier at the steps. The latter contribution is strongly reduced when near-surface step dislocations are imaged.