Load dependence of lateral force and energy dissipation at NaF(001) surface

We report the load dependence of the lateral force and the energy dissipation occurring at a tip-NaF(001) interface. Clear sublattice periodic maps of the lateral force consisting of large and small peaks appear at loading forces below tens of pN and even at negative loading forces. As loading force is increased, only large peaks remain, representing lattice periodicity. The behavior of the stick-slip lateral fords is completely consistent with that of the energy dissipation calculated from the frictional loops. At a load of around 6 nN, an abrupt increase in the lateral force occurs, causing a large deformation of the surface. The load dependence of the lateral force is attributed to that of the contact area between the tip-NaF(001) interface. (C) 2000 Elsevier Science B.V. All rights reserved.