Contrast mechanism in non-contact SFM imaging of ionic surfaces

We analyse the mechanisms of contrast formation in NC-SFM imaging of ionic surfaces and calculate constant frequency shift scanlines of the perfect surfaces of NaCl and MgO. Non-contact SFM operation is modelled in a perturbed oscillator model using an atomistic simulation technique for force–field calculations. We demonstrate that the contrast in NC-SFM imaging of ionic surfaces is based on the interplay between the van der Waals interaction and the electrostatic interaction of the tip with the surface potential and the local surface polarisation induced by the tip. The results emphasise the importance of the tip-induced relaxation of the surface ions in the tip–surface interaction and image contrast. q1999 Elsevier Science B.V. All rights reserved.