Determining surface properties with bimodal and multimodal AFM
  Conventional dynamic atomic force microscopy (AFM) can be extended to bimodal and multimodal AFM in which the cantilever is simultaneously excited at two ore more resonance frequencies. Such excitation schemes result in one additional amplitude and phase images for each driven resonance, and potentially convey more information about the surface under investigation. Here we present a theoretical basis for using this information to approximate the parameters of a tip-surface interaction model. The theory is verified by simulations with added noise corresponding to room-temperature measurements. 
Daniel Forchheimer, Stanislav S. Borysov, Daniel Platz, David B.   Haviland
cond-mat.mes-hall