Crystal sensor for microscopy applications

We report a force sensor based on a quartz crystal that is used for measuring nanoscale topographic
images. The crystal is a length-extensional mode oscillator with a resonant frequency of about 650
kHz. Compared to 33 kHz tuning forks, such crystal sensors have a much higher resonance
frequency, which allows for high force sensitivity and a fast response time. The crystal sensor is
operated in the shear-force mode, with the probes vibrating parallel to the sample surface. The
tip-sample interaction during operation is estimated to be less than 300 pN.