Viscosity dependence of electrochemical etching for gold tip fabrication

We suggest an electrochemical etching method with viscous etchant to enhance the sharpness of tip of scanning probe microscope. The viscosity of the etchant mixed with HCl solution and glycerol was used as a control parameter in addition to the voltage applied to the tip. In order to improve the sharpness of the tip, a nano-scale meniscus formed between the end of the tip and the liquid level was used. The shapes, aspect ratios, and radii of tips were measured depending on the concentration of the etchant. It was found that the tip etched with the mixed liquid with glycerol was sharper than the tip with the pure HCl solution. This can be explained by the fact that the meniscus formed by viscous liquid is maintained with a thinner diameter and causes final etching until the meniscus bridge is ruptured. ► Au tip with about 10 nm apex radius was obtained using electrochemical etching. ► Addition of glycerol of HCl solution improves tip sharpness. ► Optimum condition of the glycerol concentration was 15 wt%. ► When glycerol concentration is too excessive, blunt tip is fabricated.