Effects of Atomic Arrangement at Tip Apex and Tip-Sample Distance on Atomic Force Microscopy Images: A Simulation Study

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.