AN EASY-TO-USE NON-OPTICAL SHEAR-FORCE DISTANCE CONTROL FOR NEAR-FIELD OPTICAL MICROSCOPES

We present an easy-to-use non-optical shear-force detection system for tip-sample distance control in scanning near-field optical microscope s. The fibre tip is fixed in a four-segmented piezo-tube by a polymer, Polyisobutylene, which couples the tip stiffly to the piezo at freque ncies of 10 kHz or more at room temperature. One segment of the piezo- tube excites the fibre tip in resonance, while the other three segment s detect the tip vibration in the manner of a piezo-microphone. When t he tip is damped by shear forces the induced voltage at the three segm ents changes and can easily be detected with a lock-in amplifier. Furt her our method allows a fast and reproducible tip exchange with minor adjustments of mechanical ol electrical components. We demonstrate the performance of our distance control on a holographically fabricated l ine pattern with 417 nm lattice spacing and 10 nm height. A height res olution of better than 1 nm is demonstrated. (C) 1996 American Institu te of Physics.