High throughput aperture near-field scanning optical microscopy

This article presents a simple measurement setup for characterization of a combined near-field scanning optical and atomic force microscopy (NSOM/AFM) using an aperture Si based probe. A technological approach has been found for the fabrication of a miniature aperture at the apex of a SiO₂ tip on a Si cantilever for NSOM using a "low temperature oxidation and selective etching" (LOSE) technique. The optical transmission efficiency (throughput) of the fabricated probe was measured to be about 10^-2 when the aperture size was approximately 100 nm, which is several orders of magnitude higher than that of conventional optical fibers and is also higher than other published throughput on micromachined tips due to a large curvature angle of the SiO₂ tip. An extension of the LOSE technique for the fabrication of a tip with a tiny aperture having a metal nanowire at the center of the aperture for a multipurpose NSOM probe is also presented. Using the proposed measurement setup and the fabricated probe, NSOM and corresponding AFM images in contact and tapping modes of several surfaces are obtained.