Dual actuation for high-bandwidth nanopositioning

The imaging speed of atomic force microscopes (AFM) is limited by the bandwidth of the feedback loop to measure the sample topography. In contact mode as well as tapping mode operation, this feedback loop is crucial to control and minimize the force between the probing tip and the sample, which is done by controlling the vertical tip sample distance via a piezo actuator. For fast imaging, control of the probe-sample distance requires a high closed-loop bandwidth. To achieve this goal without reducing the existing positioning range, a second, high-bandwidth actuator is introduced to an existing AFM setup. A model-based controller is designed and implemented to improve the bandwidth of the primary feedback loop for tapping mode and contact mode imaging. For highest imaging bandwidth in contact mode, an accessory high-performance controller is designed and implemented on the dual actuated AFM system. The improved performance of the new control-system is experimentally demonstrated.