FRICTION FORCE MICROSCOPY INVESTIGATIONS OF POTASSIUM HALIDE SURFACESIN ULTRAHIGH-VACUUM - STRUCTURE, FRICTION AND SURFACE MODIFICATION

Friction force microscopy measurements on the vacuum-cleaved (001) sur faces of RF, KCl and KBr have been carried out. All surfaces exhibit a tomically flat terraces with monatomic steps aligned preferentially al ong low-index lattice directions. Stick-slip lateral forces with the l attice periodicity are observed on all surfaces. Tip-sample contact cr eates higher friction domains on the terraces of all three materials. The structure, topography and degree of friction force contrast of the se 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 str uctural changes created by low load tip-sample contact on these relati vely soft materials.