  A new approach, called Adaptive Q-control, for tapping-mode Atomic Force
Microscopy (AFM) is introduced and implemented on a home-made AFM set-up
utilizing a Laser Doppler Vibrometer (LDV) and a piezo-actuated bimorph probe.
In the standard Q-control, the effective Q-factor of the scanning probe is
adjusted prior to the scanning depending on the application. However, there is
a trade-off in setting the effective Q-factor of an AFM probe. The Q-factor is
either increased to reduce the tapping forces or decreased to increase the
maximum achievable scan speed. Realizing these two benefits simultaneously
using the standard Q-control is not possible. In adaptive Q-control, the
Q-factor of the probe is set to an initial value as in standard Q-control, but
then modified on the fly during scanning when necessary to achieve this goal.
In this paper, we present the basic theory behind the adaptive Q-control, the
electronics enabling the on-line modification of the probe's effective
Q-factor, and the results of the experiments comparing three different methods:
scanning a) without Q-control, b) with the standard Q-control, and c) with the
adaptive Q-control. The results show that the performance of the adaptive
Q-control is superior to the other two methods.
