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 su rfaces of NaCl and MgO. Non-contact SFM operation is modelled in a perturbe d oscillator model using an atomistic simulation technique for force-field calculations. We demonstrate that the contrast in NC-SFM imaging of ionic s urfaces is based on the interplay between the van der Waals interaction and the electrostatic interaction of the tip with the surface potential and th e local surface polarisation induced by the tip. The results emphasise the importance of the tip-induced relaxation of the surface ions in the tip-sur face interaction and image contrast. (C) 1999 Elsevier Science B.V. All rig hts reserved.