The control of higher modes in atomic force microscopy

Strong nonlinear interactions between the cantilever tip and sample may result in coupling of the cantilever modes, which may result in image artefacts. Such observations have been made in liquid AFM [1] and contact mode AFM [2, 3]. There are currently very few solutions to address this problem. While the displacement sensor can be calibrated to ignore contributions from the higher modes, this approach lacks robustness [4]. To mitigate these effects, we propose the application of modulated-demodulated control to suppress the higher modes. The modulated-demodulated control technique is advantageous as it reduces the bandwidth requirements of the baseband controller, simplifying the implementation of high-bandwidth controllers [5].