A team of researchers from the University of Basel in Switzerland and from Karl-Franzens University in Graz, Austria, has produced aperture probes for near-field optical microscopy using controlled all-solid-state electrolysis. The technique, which yields probe tips with aperture diameters of less than 50 nm, avoids the problems associated with alternative production methods such as shadowing, punching, focused ion beam milling and wet electrolytic tip demetallization.

In a demonstration that they reported in the July 30 issue of Applied Physics Letters, the researchers employed a tube-etched optical fiber as the core of the probes, which they coated with a 350-nm-thick layer of silver. Amorphous silver metaphosphate-iodide served as the solid electrolyte. A photomultiplier tube monitored the flux of 532-nm laser light transmitted through the fiber and probe to determine when the demetallization process should be terminated.