The underlying mechanisms of image distortions in atomic force microscopy (AFM) with CO-terminated tips are identified and studied in detail. AFM measurements of a partially fluorinated hydrocarbon molecule recorded with a CO-terminated tip are compared with state-of-the-art ab initio calculations. The hydrogenated and fluorinated carbon rings in the molecule appear different in size, which primarily originates from the different extents of their π-electrons. Further, tilting of the CO at the tip, induced by van der Waals forces, enlarges the apparent size of parts of the molecule by up to 50%. Moreover, the CO tilting in response to local Pauli repulsion causes a significant sharpening of the molecule bonds in AFM imaging.
Keywords: NC-AFM; Single molecule.