We investigated the load dependence of two-dimensional atomic-scale fr
iction between a MoS2 surface and a Si3N4 tip We found that the amplit
ude of the frictional force hysteresis is determined by the effective
adhesive radius itself. Besides, we observed nearly zero kinetic frict
ional force at the normal load of 2.3 X 10(-8) N. The load dependence
of the effective adhesive radius suggests that the appearance of the n
egative frictional force correlates clearly with the load dependence.