Effect of surface tension on self-termination in Au tip fabrication for tip-enhanced Raman spectroscopy

The effect of surface tension on the fabrication of Au tips was investigated. When using a 12 M HCl aqueous solution, the etching process did not consistently self-terminate after the lower part of the wire dropped, resulting in the poor reproducibility of the tip sharpness. However, using an ethanolic solution of 12 mol/l HCl, a self-terminating etching process was always observed, resulting in the improved reproducibility of sharp tips. We attribute this to the reduced surface compared to that of aqueous HCl. The obtained tips were used in tip-enhanced Raman spectroscopy experiments, in which significant signal enhancement was observed.