MECHANICAL OSCILLATOR TIP-TO-SAMPLE SEPARATION CONTROL FOR NEAR-FIELDOPTICAL MICROSCOPY

A nonoptical system for controlling the tip-to-sample separation in a near field scanning optical microscope is described. It consists of a tapered aluminum-coated fiber glued to a high-Q Si paddle mechanical o scillator. The paddle is driven at one of its resonances by a capaciti vely coupled electrode, and the amplitude of oscillation is detected t hrough a second electrode. This resonant amplitude, which varies as th e tip approaches the surface, is used as a feedback signal to control the separation between tip and sample. A separation stability better t han 0.8 nm is achieved in the 0-200 nm range. We present a complete ch aracterization of this system and demonstrate its capabilities with sh ear-force images of two samples. (C) 1997 American Institute of Physic s.