Oral SUBLATTICE IDENTIFICATION BY NON-CONTACT AFM ON THE (001) SURFACE OF A ROCKSALT-TYPE CRYSTAL

Dynamic force microscopy has proven able to achieve true atomic resolution on the surface of different materials in UHV, insulators in particular [1]. Owing to imperfect knowledge about the structure and composition at the apex of the imaging tip, it is, however, difficult to assign observed features to specific atomic sites. On ionic crystals, a common approach is to compare experimental images with simulations relying on plausible models of the tip apex and fitted interionic potentials. Thus, on the CaF2(111) surface, F ions at inequivalent sites could be distinguished [2]. On the (001) cleavage plane of crystals with the rocksalt structure, however, one kind of ion is imaged as a maximum, and the other kind as a minimum. Owing to the high symmetry, it was deemed impossible to determine which sublattice is imaged because the sign of the electrostatic potential near the tip apex is not known a priori.