Simulation of Atomic Force Microscopy Image Variations along the Surface Normal: Presence of Possible Resolution Limit in the Attractive Force Range

Abstract

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.

Simulation of Atomic Force Microscopy Images of Cleaved Mica Surfaces

“…Figure 4 shows the simulated results for each of the three tip orientations. Weaker applied force means longer tip-to-sample distances, and our earlier calculations 13,14 indicated that this necessarily means the loss of resolution. For the single-atom tip (θ s orientation) no resolution loss is observed, and the atom-resolved image is still obtained (Figure 4a).…”

“…Loading force apparently has a strong influence on the observed images, by governing the tip−sample distance. The distance in turn governs the resolution, particularly for isotropic potentials. , Thus these images may take various forms depending on the applied force, or tip−sample distance. It should be noted that the absolute value of the force examined in this simulation is not important, since it may strongly depend on the size of the simulated tip …”

“…For the simulations a recently developed AFM simulator ACCESS (AFM simulation code for calculating and evaluating surface structures) ,, was employed under two-dimensional periodic boundary conditions parallel to the sample surface. The forces acting between the atoms in the tip and those in the sample were calculated by using the differential of the following interatomic potential function…”

Determination of Extraframework Cation Positions and Their Occupancies on Heulandite (010) by Atomic Force Microscopy

“…A simulation of AFM imaging of the surface was performed following a previously reported method, using an algorithm similar to the previously developed AFM simulator ACCESS − under two-dimensional periodic boundary conditions parallel to the sample surface. With a model AFM tip consisting of a Si(OH) 4 cluster the topmost cleaved plane of heulandite(010) was scanned.…”

Atomic force microscopy imaging of chloride ions adsorbed on etched polycrystalline copper in dilute HCl

“…3(a)) gives a better atomic contrast, which is in good agreement with results from simulation. 6,7 The Fourier transform of the unfiltered image shown in Fig. 3(a) is given in Fig.…”