Choosing a preamplifier for tuning fork signal detection in scanning force microscopy

In scanning probe microscopy, it is critical to maintain small probe sample separations for high resolution imaging. Quartz crystal tuning forks are typically used for detecting shear forces in near-field scanning optical microscopy and normal forces in other atomic force-related microscopies. In this article we compare several tuning fork based detection schemes to determine which solution gives the best signal to noise ratio. The high impedance and low signals produced by the tuning fork necessitate care in selection of an appropriate preamplifier. We find that a carefully guarded voltage preamplifier sensing a mechanically driven tuning fork performs the best, but an electrically driven fork with a current preamplifier offers simpler construction with only 25% lower signal to noise ratio on average. (C) 2004 American Institute of Physics.