Production of gold tips for tip-enhanced near-field optical microscopy and spectroscopy: analysis of the etching parameters

In this paper, we analyze in detail the etching parameters that are used for manufacturing gold tips for tip-enhanced near-field optical microscopy and spectroscopy. From the current variation versus time, we first demonstrate that the sharpest tips are obtained if the etching is stopped at a specific time where the curve presents an inflexion point. We then analyze the influence of the concentration of the etching solution and the applied voltage on the roughness and the tip apex. As a result, we propose a set of parameters allowing for reproducible production of gold tips with 20 nm radius of curvature