Systematic study of electropolishing technique for improving the quality and production reproducibility of tungsten STM probe

Based on the systematic study of electropolishing process, an improved tungsten STM probe fabrication technique has been presented. The proper combination of pulse current and the electrolyte concentration is explored for the elimination of impurities and achieves high quality probes with ultra-smooth surfaces. An optimized immersion depth of tungsten wire in electrolyte is proposed for the purpose of realizing the probe with sharp apex as well as high aspect ratio structure. A control strategy for determining the power-off instant during the procedure of electropolishing is developed which will facilitate the fabrication of probe with exponential contour as well as ultrasharp tip. The proposed technique and process are experimentally confirmed to have advantages for the STM probe fabrication of the stabilized stylus contour, typically with apex radius of 30 nm and the yield rate reaches as high as 85%.