Scanning near-field optical microscopy using piezoelectric cantilevers

Microfabricated cantilevers for atomic force microscopy (AFM), used as scanning near-field optical microscopy (SNOM) probes, have remarkable advantages because the fabrication process is well established. In addition, the SNOM probe can be combined with an atomic fore microscope, which is capable of detecting various surface properties. However, the optical method for measuring the deflection of the cantilever often disturbs the detection of weak evanescent light. We have developed a new SNOM probe using a microfabricated cantilever with a piezoelectric thin film as an integrated deflection sensor so that any optical measurements for the deflection are not required. The cantilever is made of Si with deposited layers of Pt/lead ziconate titanate (PZT)/Pt and an SiN hollow pyramidal tip at the end. The light scattered by the tip can transmit the cantilever when the PZT cantilever is brought in close proximity to a sample surface. The tip-to-sample distance is regulated using the piezoelectric current while the cantilever is vibrated at its resonance frequency. Both topographic and optical images were obtained successfully by the new SNOW probe.