Giant Atomic Corrugations on Layered Dichalcogenides Investigated by AFM/LFM

Giant atomic corrugations of up to 10 A were observed on different layered dichalcogenides (MoSe2, WSe2, NbSe2 and WS2 ) by atomic force microscopy (AFM). For the case of NbSe2, the dependence of the corrugation values on the experimental parameters is investigated in more detail. It is found that the existence of these increased values of the atomic corrugation is closely correlated with lateral forces between cantilever tip and sample surface. The cross-sections of the images exhibit a sawtooth profile, indicating atomic-scale stick and slip processes. At the beginning of a scan line, distorsions frequently occur, and a hysteresis is observed between forward and backward scan. A dependence of the atomic corrugations on the angle between the scanning direction and the directions of symmetry of the lattice is found. With increasing normal force between tip and sample, the atomic corrugation increases by about 60% between 108 N and 107 N. For still higher forces, the corrugation monotonically decreases. An explanation of the enlarged corrugation values is proposed on the basis of cantilever bending due to atomic scale stick and slip movements.