Abstract
Friction and pull-off forces were measured between an atomic force microscope (AFM) probe made of Si3N4 and submicron asperity arrays on a single-crystal tungsten plate, a silicon wafer, and a platinum film. A focused ion beam was used to produce the two-dimensional asperity arrays. The tip of the AFM probe had a flat, square surface measuring 0.7×0.7 μm2. The pull-off force was proportional to the curvature radius of the asperity peak, but was not affected by micro-roughness at the peak. The friction force was proportional to the pull-off force. These findings suggest that the Laplace pressure of the condensed water was the predominant pull-off force and that the pull-off (adhesion) force worked as an external normal load for the friction. The friction coefficients calculated by regarding the pull-off force as an external normal load were compared for the platinum and silicon patterns, and this proved that the friction coefficient on the silicon was about twice as high as on the platinum.
