HIGH-CONTRAST PIEZOELECTRIC FIBER RESONANCE DETECTION FOR NEAR-FIELD OPTICAL MICROSCOPY

We describe a simple, piezoelectric shear-force detection for controll ing the tip-sample distance in near-field optical microscopes. The fib er is glued to a V-shaped piezoelectric cantilever and the assembly is fixed to a piezoelectric plate. The piezoelectric plate excites the f iber at resonance, while the piezoelectric cantilever of small mass de tects the fiber motion with a high sensitivity. When the fiber approac hes within, typically, 10-20 nm above the sample, shear forces cause t he signal to reduce. The only signal processing before injecting it in to the feedback loop is demodulation by a lock-in amplifier. The high signal-to-background allows the fiber resonance to be identified easil y. We demonstrate the performance of our system with shear-force image s of two test patterns. (C) 1997 American Institute of Physics. [S0034 -6748(97)05010-7].