LAUSR

We demonstrate a series of experiments to find optimized electrochemical etching condition for fabricating gold nanotip, using square-wave voltage as a bias and using hydrochloric acid diluted by acetone as an etchant. We confirmed that the dilution ratio of 3: 1 between hydrochloric acid and acetone give the smallest tip apex diameter which reproduces our previous result. More importantly, by varying applied bias condition and immersion depth of the platinum ring used as a cathode inside the etchant, we found that the smaller tip apex diameter is achieved when both the amplitude and duty cycle get higher. The success rate, which we define the number of tips having meaningfully less diameter out of total number of tried tips, is also discussed.