Computer-controlled fabrication of ultra-sharp tungsten tips

In order to monitor the end-point current during electrochemical etching, an analog to digital converter circuit aided by a personal computer has been setup. At the moment the lower part of the needle drops off during the etching process, a maximum current change across the reference resistor is detected by the PC interface card and the applied voltage is then cut off within a few milliseconds. Using these circuits to control the etching time, our experiment has been able to fabricate an ultra-sharp tip of similar to 200 Angstrom radius with a higher reproduction rate and reliability than the conventional method. (C) 1998 American Vacuum Society.