True atomic resolution under ambient conditions obtained by atomic force microscopy in the contact mode

A step edge on the (0001) cleavage plane of the layered dichalcogenide 2H-n iobium diselenide (2H-NbSe2) has been investigated by contact-mode atomic f orce microscopy (AFM) in air. Both the terraces and the monolayer step itse lf were reproducibly imaged at atomic resolution in the repulsive-force reg ime at forces between tip apex and sample of the order of 10(-9) N. Several kinks were also imaged at atomic resolution. Details of the atomic registr y of subsequent Se-Nb-Se sandwich layers as well as the arrangement of the individual atoms at the kink sites were resolved. The results are in perfec t quantitative agreement with the lattice structure known from X-ray analys is and indicate that true atom-by-atom lateral resolution of microscopic de fects is feasible by AFM in the contact mode and under ambient conditions.