Calibration and set-up of 100 kHz shear-force distance control for near- field optical microscopy

We report on the set-up and calibration of a sensitive and fast non- optical shear-force distance control using 100 kHz quartz tuning fork oscillators. The shear-force detector was calibrated with a Michelson interferometer. Vibration amplitudes of the near-field probe were typically 0.3 nm when imaging a sample topography. Assuming that shear-force damping was due to friction, the interaction forces between tip and sample were estimated to be ≤1 nN. With the short relaxation times of the 100 kHz oscillators scan rates up to 100 μm/s could be realised. Aluminium/glass test samples were imaged and demonstrated sensitive and stable feedback operation and subwavelength resolution in transmission near-field images. Application of our set-up to fluorescing biological samples is discussed.