Fig. 1

Time controlled electrochemical etching of tungsten wire in sodium hydroxide (NaOH) solution. a Schematic for the electrochemical etching along with the feedback circuit composed of a high-speed voltage comparator. b Tip height as a function of the immersion depth and corresponding SEM images. c Tip height as a function of the NaOH concentration and corresponding SEM images. d Typical time-dependent voltage change monitored during the electrochemical etching