Taking into account the Coulomb and exchange forces, atomic force microscopy (AFM) and lateral force microscopy (LFM) simulations were performed for a Si(OH) 4 tip and a cleaved mica surface under planer two-dimensional periodic boundary conditions. Imaging of the individual oxygen atoms in hexagonal oxygen rings and/or K + ions on a cleaved mica surface strongly depended on the tip orientation and the applied force. Experimentally obtained AFM images of cleaved mica surfaces were interpreted in terms of the present simulation results.

Using a newly developed atomic force microscopy (AFM) simulator ACCESS (AFM simulation code for calculating and evaluating surface structures), effects of the atomic arrangement at the tip apex and tip-sample distance on AFM image resolution were examined. A tip which has an atom protruding at its apex and is scanning in the repulsive force range is found to be necessary for obtaining atomically resolved AFM images. The second atomic layer of the tip determines the force characteristics of the system, as well as the AFM image phase shift. Since in actual AFM systems these two effects are convoluted, it is apparent that scanning under the same applied force does not necessarily mean the same tip-sample distance or the same image resolution, unless one is sure that the atomic arrangement at the proximity of the tip apex is the same. It is also found that surface point defects mirror the atomic arrangements of the tip apex in the AFM images, both in attractive and repulsive force ranges, indicating their possible use in tip apex evaluation at the atomic level.

Variations of atomic force microscopy (AFM) images as tip-sample distance is varied were examined using a newly developed AFM simulation code ACCESS (AFM simulation Code for Calculating and Evaluating Surface structures) with a Morse-type pairwise potential. A model system consisting of a single atom tip (an “ideal" AFM tip) and a face-centered cubic (fcc) (100) surface with or without point defect showed perfect atomic resolution when scanning was performed in the repulsive force range. In the attractive force range, image contrast inversion was observed twice with the increase of tip-sample distance. Simulation on the point defect surface indicated that this inversion is due to a collective force from more than one atom being imaged as one bright spot. Exact correspondence between the sample surface registry and the simulated image in this force range appears to be coincidental.

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