Figure 1.

(a) Schematic diagram of the homemade electrochemical etching setup. A gold wire is connected to the positive pole (anode) of an arbitrary waveform generator to attract chloride ions and to initiate gold ionization. A platinum loop is connected to the negative pole (cathode) of the wave function generator. (b–e) SEM images of the etched gold tips fabricated with various concentrations of ethanol and HCl solution. (b) Only HCl solution. (c) HCl solution:ethanol = 3:1, (d) 2:1, and (e) 1:1 (Scale bar of right upper applies to all SEM images in b–e).