Double-resonance probe for near-field scanning optical microscopy

A surface-contact transducer is developed for scanning probe microscopes, whose operating principle is based on the coincidence between the resonance frequency of a 32 kHz quartz tuning fork and that of the probe attached to it. This allows the transducer to have a high quality factor and, if the vibration amplitude of the probe tip exceeds that of the tuning fork prongs, materially improves its force sensitivity. The resonance transducer proposed by us has an experimentally verified force sensitivity of 8 pN (rms) in the 300 Hz frequency band, which is of the same order of magnitude as the sensitivity of atomic force microscope (AFM) cantilever sensors. The manufacture of such transducers equipped with optical-fiber probes for near-field scanning optical microscopy and with tungsten probes for AFM is described as an example. (c) 2006 American Institute of Physics.