An improved control technique for the electrochemical fabrication of scanning tunneling microscopy microtips

The electrochemical etching technique has been widely used in the fabrication of microtips. In this article, an improved feedback control technique for the dc electrochemical fabrication of scanning tunneling microscopy microtips is presented. Distinguished from the conventional control techniques, this newly developed method directly uses the etching current as the only control signal instead of comparing it with the reference current. Therefore, the control process is more accurate. The tungsten tips with radius of curvature down to 20 nm can be produced reproducibly. By varying the cutoff time of the control circuit, tips with different radii of curvature can be fabricated.