Digital image processing for measuring 2D vibration amplitudes with subpixel resolution: application to the quartz tuning fork

We present digital image processing techniques for measuring the vibration amplitude of a 32 kHz quartz tuning fork in the fundamental flexural mode, torsional mode and first harmonic flexural mode. The objective is to estimate the ultimate resolution of shear force scanning probe microscopy in which such a tuning fork is used for vibrating a tip over the surface being analyzed: we observe vibration amplitudes of around 350 nm/V for the fundamental flexural mode and 75 nm/V for the first flexural overtone. These values provide a fundamental limitation -beyond the probe tip size -of the spatial resolution of shear force scanning probe microscopes.