Self-lubrication in scanning-force-microscope image formation on ionic surfaces

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Abstract
The mechanisms of and conditions required for true atomic resolution remain the focus of scanning force microscopy (SFM). We present a theoretical model of SFM using a molecular-dynamics method for the calculation of the interaction between a crystalline sample and a tip nanoasperity, combined with a semiempirical treatment of the mesoscopic van der Waals attraction between tip and surface, and the macroscopic parameter of cantilever deflection. The main features of the SFM experiment were modeled, including force versus distance curves at various tip positions on the surface, and scanning of a perfect LiF surface in contact regime with a repulsive force of 1–2 nN. It is shown that tip contamination due to adhesion to the surface atoms may promote periodic SFM imaging, if the adsorbed surface material makes stable structures on the tip. We demonstrate that the adsorbed cluster can adjust itself to conditions of scanning by exchanging atoms with the surface and changing its structure. We believe that this dynamic “self-organization” of the surface material on the tip during scanning could be a general effect which may explain why periodic surface images are often obtained using a variety of tips and large tip loads.