The role of the tip in non-contact atomic force microscopy dissipation images of ionic surfaces

In this paper we use simulations to investigate the role of the tip in nc-AFM measurements of dissipated energy. Using a virtual AFM we simulate the experiment focusing on the atomic scale energy dissipation on an NaCl(100) flat surface. The non-conservative interaction was treated with the theory of dynamic response and all the calculations were carried out using an atomistic model; several sets of tips were tested using ionic crystals (NaCl, KBr, MgO), each in different configurations (ideal, vacant, divacant, doped). Using an MgO-doped tip we were able to calculate a dissipation signal comparable to what is typically measured in experiments. It was not possible to see any dissipation with ideal tips, although they still have a significant interaction with the surface and give atomic contrast in the frequency shift signal. The effect of the scanning speed on measured frequency shift and dissipation is also calculated and discussed.