Reproducible optical fiber tips for photon scanning tunneling microscopy with very small (<5°) cone angle

Sharp optical fiber tips for photon scanning tunneling microscopes (PSTM's) have been fabricated by employing a new alternative technique for etching multimode optical fibers. The tip diameter is less than 30 nm, while the cone full-angle can be as sharp as 3 degrees. To the knowledge of the authors, such tips are the sharpest reported up to now. Measurements, with 19 tips, of the evanescent wave decay distance produced by frustrated reflection of light on a same sample, show good reproducibility, Furthermore, the PSTM images, taken with the new tips, are very sharp and fit with images of the same sample obtained with an atomic force microscope (AFM).