Feed-forward compensation for high-speed atomic force microscopy imaging of biomolecules

High-speed imaging by atomic force microscopy (AFM) requires the implementation of a fast control of tip-surface distance to maintain a constant interaction force. In particular, a well-controlled low load force is essential for observing soft biological molecules without causing damage to the sample. The accurate control of tip-surface distance where only feedback control is used is intrinsically difficult particularly for fast scanning. Here, we demonstrate that the combination of feedback and feed-forward control is useful for a more accurate distance control. We evaluate the bandwidth performance of the closed loop with and without feed-forward compensation using a model AFM system.We show that the combination of feedback and feed-forward control yields a greater than two fold improvement in bandwidth. We have applied this technique to the observation of myosin V and actin filaments at a high scanning rate.