Friction force microscopy investigations of potassium halide surfaces in ultrahigh vacuum: structure, friction and surface modification

Friction force microscopy measurements on the vacuum-cleaved (001) surfaces of KF, KCl and KBr have been carried out. All surfaces exhibit atomically flat terraces with monatomic steps aligned preferentially along low-index lattice directions. Stick-slip lateral forces with the lattice periodicity are observed on all surfaces. Tip-sample contact creates higher friction domains on the terraces of all three materials. The structure, topography and degree of friction force contrast of these domains is material dependent. The dependence of friction upon load generally does not coincide with the behavior expected for an elastic contact. We propose that the observed domains result from surface structural changes created by low load tip-sample contact on these relatively soft materials.