Sharpening Conical Tungsten Nanotips in KOH Solution under Laser Irradiation

Laser-enhanced chemical etching with a 532 nm neodymium-doped yttrium aluminum garnet pulsed laser in KOH solution was used for sharpening conical tungsten nanotips which were prefabricated with a conventional electrochemical etch. The laser irradiation was incident axially on the tip apex. Due to different light absorption mechanisms by objectives in different sizes, the laser irradiation generates a controllable temperature gradient profile from the tip apex to the tip base. In the KOH solution, the etching rate varies with the temperature profile along the tip axis. The tip apex radius was greatly reduced, with the shape and aspect ratio in good control.