Near-field optical apertured tip and modified structures for local field enhancement

We present experimental measurements and simulation of the spatial distribution of near-field light at the aperture of a Si micromachined near-field scanning optical microscopy (NSOM) probe. A miniature aperture at the apex of a SiO₂ tip on a Si cantilever was fabricated with the low temperature oxidation and selective etching technique. An optical transmission efficiency (optical throughput) of the fabricated probe was determined to be approximately 10^-2 when the aperture size was approximately 100 nm, which is several orders of magnitude higher than that for conventional optical fibers. A threedimensional finite difference time domain (FDTD) simulation shows that the near-field light is well confined within the aperture area with a throughput of 1% for a 100-nm aperture, which is in good agreement with the measurement. The spatial distribution of the near-field light at an aperture of 300-nm diameter shows a full width at half-maximum of 250 nm with a sharp peak that is nearly 60 nm wide. The 2.4% throughput for a 300-nm aperture was estimated based on the measured spatial distribution of the near-field light that is almost the same as the experimental result. We also present the initial results of the fabrication of high throughput coaxial and surface plasmon enhancement NSOM probes.