ATOMIC-SCALE CONTRAST MECHANISM IN ATOMIC FORCE MICROSCOPY

Despite the early success of atomic force microscopy in imaging atomic structures on layered materials, much of the hope and expectation for the high resolution capability of this method have been subverted by puzzling experimental results and a poor understanding of the basic contrast mechanism. The fact that very high repulsive forces can be applied between the tip and the sample without losing atomic resolution has led to several different explanations of the imaging process. These include multiple tip-sample contact imaging, large elastic deformations of the sample, and friction-dominated image formation. Until very recently it was only possible to atomically resolve materials having layered structures, such as HOPG, BN, MnPS3, mica, TaS2 and TaSe2. Here, we compare those images with the ones collected from surfaces of the predominantly ionic crystals LiF and PbS. Based on the comparison of these two classes of imaged materials, contrast mechanisms are discussed.