Electronic driver with amplitude and quality factor control to adjust the response of quartz tuning fork sensors in atomic force microscopy applications

Quartz tuning fork-based sensors are self-sensing probes that are gaining popularity in atomic force microscopy. They do not need a laser-photodiode system and they have a higher quality factor in liquid than standard cantilevers. However, the main limitation of tuning fork probes is that they are usually handmade because no commercial probes suitable for a wide range of experiments are available. The handmade devices show considerable variation in dynamic response, thereby hindering the repeatability of experiments. To overcome this problem, here we develop an electronic driver to simultaneously control the quality factor (Q) and the oscillation amplitude (A) of the device. The driver provides clear advantages over classical Q-control modules where the amplitude of oscillation is modified when the Q factor is changed. Direct measurements on a commercial interferometer showed that the effective Q factor can be adjusted to experimental requirements while maintaining the mechanical amplitude of oscillation constant. Experimental amplitude vs. distance curves confirm that our driver achieves an equivalent dynamic response from distinct handmade sensors (with varying mechanical characteristics) by means of electronic adjustment. The driver is a simple but effective method to ensure the same measurement conditions with a range of quartz tuning fork probes and also the reliability and repeatability of experiments.