Increasing shear force microscopy scanning rate using active quality-factor control

The use of an active quality-factor control device has been demonstrated to increase the scanning rate of a shear force microscope by lowering the quality factor of the oscillating probe. Shear force microscopy (often used in combination with scanning near-field optical microscopy) requires slow scanning rates due to the long $(>1 ms)$ time constant of the oscillating element (optical fiber or tuning fork). By electronically reducing the quality factor of the probe, it was possible to tune the time constant and correspondingly reduce the overall scanning time by a factor of 4. It was also seen that probes with high quality factors could manifest an unstable behavior; by reducing the quality factor of the probe, it was possible to increase the signal-to-noise ratio and so improve the imaging resolution. Deoxyribonucleic acid molecules deposited onto mica and imaged in air were used to demonstrate the technique.