Fabricating ultra-sharp tungsten STM tips with high yield: double-electrolyte etching method and machine learning

The double-electrolyte etching method is a simple and effective way to fabricate ultra-sharp scanning tunnel microscopy (STM) tungsten tips. However, it is still challenging for this method to get ultra-sharp tungsten tips with high yield. In this work, significant enhancing of the yield is presented through optimized etching parameters as follows: temperature of 26 °C, applied voltage 7.5 V, electrolyte concentration 4 mol L−1 and length below the liquid lamellae of 2 mm. Under these conditions, the smallest tip radius is around 8 nm and the yield (radius