Unambiguous interpretation of atomically resolved force microscopy images of an insulator

The (111) surface of CaF2 was imaged with dynamic mode scanning force micro scopy and modeled using atomistic simulation. Both experiment and theory sh owed a clear triangular contrast pattern in images, and theory demonstrated that the contrast pattern is due to the interaction of a positive electros tatic potential tip with fluorine ions in the two topmost surface layers. W e find a good agreement of position and relative height of scan line featur es between theory and experiment and thus establish for the first time an u nambiguous identification of sublattices of an insulator imaged by force mi croscopy.