Preparation and characterization of electrochemically etched W tips for STM

We have investigated methods for cleaning de-etched polycrystalline tungste n tips for scanning tunnelling microscopy (STM). The cleaning methods inclu de Ar-ion sputtering, heating, chemical treatments and Ne-ion self-sputteri ng. We correlate transmission electron microscopy images of the tip, field- emission data from the tip and images of a clean Cu(111) surface to find an optimum procedure for STM imaging. Clean and sharp tips are made by sputte ring, combined with careful heating by electron bombardment. We found that optimum sputtering was obtained either by use of a 4 keV Ar-ion gun for a f ew seconds or by self-sputtering with Ne ions for a few seconds or until de capitation occurs.