Tungstate Sharpening: a Versatile Method for Extending the Profile of Ultra Sharp Tungsten Probes

The benefits of a new electrochemical etching method for the controlled sharpening of sub-micron tungsten probes are demonstrated. The proposed technique only utilizes the insulating effect of the WO₄(2-) by-product which offers more practical ways of controlling the process parameters. The electrosharpening method was fully automated through the analysis of the process current, bulk coulometry, shadowgraphs, and time lapse microscopy. Tip radii smaller than 15 nm were maintained over a wide range of controlled lengths up to 4.5 mm with conic angles of less than 1°.