Field ion microscope evaluation of tungsten nanotip shape using He and Ne imaging gases

Field ion microscopy (FIM) using neon imaging gas was used to evaluate a W(111) nanotip shape during a nitrogen assisted etching and evaporation process. Using appropriate etching parameters a narrow ring of atoms centered about the tip axis appears in a helium generated image. Etching of tungsten atoms continues exclusively on the outside of this well-defined ring. By replacing helium imaging gas with neon, normally inaccessible crystal structure of a tip apex is revealed. Comparison of the original W(111) tip (before etching) and partly etched tip shows no atomic changes at the tip apex revealing extraordinarily spatially selective etching properties of the etching process. This observation is an important step towards a detailed understanding of the nitrogen assisted etching and evaporation process and will lead to better control over atomically defined tip shapes. -- Highlights: ► Nanotips were prepared by nitrogen assisted etching and the evaporation process. ► The Etching process was monitored by field ion microscopy (FIM). ► Tip shape was evaluated by FIM using helium and neon as imaging gases. ► Etching mechanism and tip shaping were proposed based on the observation. ► Procedures for preparing different aspect ratio nanotips were described.