Oliver Payton (Bristol, UK)
Mathematical model of tapping mode AFM; comparison between theory and experiment
Abstract: A damped oscillating mass model is developed for tapping mode atomic force microscopy (AFM) which includes surface interaction via both van der Waal and meniscus forces and a realistic integral control law. Varying scan velocity, driving amplitude, amplitude set point and driving frequency independently shows that the model can capture the qualitative features of what is observed in AFM experiments both on a flat sample and a calibration grid. In particular the model correctly captures the onset of non-periodic motion even on a lat sample as first described by Hu et al 2006.
Experimental results confirm this onset and also confirm the qualitative features of the dynamics suggested by the simulations. The simulations also explain the mechanism behind this observed beating effect; that the control loop overcompensates for high gains or low amplitude set points.
The implications of these dynamics are explored for the accurate reproduction of the calibration grid, leading to recommendations on the effective use of AFM in order to avoid these unwanted artefacts.