Piezoelectrical shear-force distance control in near-field optical microscopy for biological applications.

We present a piezoelectrical shear-force distance control setup for scanning near-field optical microscopy. The setup is compact and tip exchange is easy. The topographical sensitivity is comparable to optical feedback systems. With an acceptable vibration amplitude of 5-10 nm we obtained a topographical resolution of 5 pm/square root of Hz. Because there is no laser necessary for tip position feedback, there is no extraneous light to interfere with spectroscopic and other low-light level experiments. Our technique permits measurements of soft biological samples in aqueous solution, which opens up many possible applications of near-field optical microscopy in biology and medicine.