Abstract
We investigated three main advantages of the photocantilever, i.e., a microfabricated photocantilever with pn-junction type photodiode on its tip, compared to other NSOM probes. The tip of the photocantilever converts the sample-modulated evanescent light into scattered light that can be collected by the photodiode fabricated at the apex of the cantilever. We demonstrated efficient collection of the scattered light, i.e., the NSOM signal light, availability of simultaneous NSOM/AFM microscopy, and the good responsivity to visible light. The photocantilever-based NSOM signal is one order of magnitude larger than that reported for AFM-cantilever-based NSOM. The minimum detectable NSOM power that we obtained was several tens of pico watts. By locating the optical-lever laser spot for AFM regulation over 100μm from the pn-junction, the photocurrent generated by the laser spot can be reduces for NSOM measurement. This enables simultaneous NSOM/AFM using the photocantilever. The resultant NSOM lateral resolution is better than 20nm (λ/30) and vertical resolution is better than 5nm. The spectral response shows that the photocantilever responds to visible light and the spectral response has a peak at about 500nm. The photocantilever enables simultaneous near-field scanning optical microscopy and atomic force microscopy, which measure both optical and topographical distributions with nanometer-resolution.
