Preparation of a needle probe with a sharp tip and high aspect ratio geometry by an electrochemical etching method

In this study, an electrochemical etching method was used to fabricate a fine needle probe with high aspect ratio. The needle probe was made of quenched and tempered high-carbon tool steel, SK 4. The needle electrode was preformed with turning machine, and then etched in the NH₄HF₂-based etchant. Owing to deactivation at the needle tip through surface adsorption of chemical species, the tip shape and contour of preformed needle can be maintained during anodic dissolution in the etchant. The anodic dissolution behavior of the needle probe can be realized with cyclic voltammetry test and Auger electron spectrometer analysis.