Sharpening behaviour of W-wire electrodes in 10–25 wt.% NaOH solutions

A W-wire was etched in aqueous NaOH solutions to form a sharp-tipped probe for scanning tunnelling microscopy. Experimental results show that a high anodic dissolution rate of the W-wire occurred in the electrode beneath the electrolyte surface, forming a tip shape. The tip sharpness depended strongly on the etching potential in the limiting-current plateau and the NaOH concentration. Three different tip morphologies of the etched W-wires were observed: a sharp tip with a negative curvature, a stepwise tip, and a long tip with a positive curvature. The anodic dissolution behaviour of the above-mentioned tips is discussed.

Research highlights
► The anodic dissolution of a W-wire was studied in aqueous NaOH solutions.
► A sharp W tip was achieved adjacent to the etching solution surface.
► Sharpening behaviour depends strongly on the NaOH content and etching potential.
► Three different tip morphologies were seen after potentiostatic etching.