Cleavage faces of alkaline-earth fluorides studied by atomic force microscopy

An atomic force microscopy (AFM) study of the cleavage faces of CaF2, SrF2 and BaF2 is presented. On the CaF2(111) surface the elementary cleavage structure with cleavage tips has been imaged. The step heights have been determined to be multiples of 0.31 nm, the projection length of the Burgers vector of the primary glide system. Atomic resolution has been achieved in step-free regions of cleavage faces. The hexagonal surface lattice with spacings of 0.38 nm corresponds to the unreconstructed bulk lattice. The 111 surfaces of SrF2 and BaF2 are characterized by a low density of parallel cleavage steps; cleavage tips are not observed. On SrF2 surfaces the formation of erosive holes has been documented by AFM.