Diameter control of an extremely thin cylindrical microprobe by electrochemical etching

The demand for ultrathin microprobes has been growing in diverse fields such as scanning probes in scanning tunneling microscopy ~STM!, atomic force microscopy ~AFM!, and micromachining. Mechanical fabrication methods generally involve precision mechanical operation such as turning, grinding, and wire electrodischarge grinding ~WEDG!. The convenience and variety of shaping in this approach is offset by uncertainty in reproducibility, limitation of size, and thermal surface damage. Electrochemical etching has been widely used for producing sharp probes for STM and AFM. This method has many advantages to make very slender microprobes, but there exist difficulties in controlling diameter and shape. A mathematical model is derived for controlling the extremely small diameter of the microprobe in electrochemical etching. The validity of the suggested model is verified through experiments.