Researchers at Universität Münster in Germany have demonstrated a probe for near-field scanning optical microscopy that effectively doubles resolution capability without compromising brightness. They presented the triangular-aperture probe in the Nov. 18 issue of Physical Review Letters.

To fabricate the probes, the researchers break a coverslip to yield a piece of glass with a sharp corner formed by three edges, then evaporate a 100-nm-thick aluminum film on the glass and attach it to a piezoelectric tuning fork. Squeezing the sharp corner against a flat glass surface removes some of the aluminum, creating a triangular hole, and a prism on the backside of the probe focuses laser light into the structure.

In a series of experiments, a 60 x 60 x 60-nm-aperture probe displayed an optical resolution better than 40 nm and a transmission coefficient of 10^-4. The technique enables the fabrication of even smaller apertures, according to the researchers.