Effective radius of adatoms/single atom of polycrystalline W nanotip in gas field ion source

Abstract

A gas field ion source (GFIS) has several advantages such as high current density, low energy spread, and high brightness. In this study, Helium gas was used in a GFIS, generated using the field ionization and field evaporation processes. The (110) oriented three adatoms tip (TAT) and single atom tip (SAT) were prepared with its ion emission stability 9.8% and 10.1% by the nitrogen field-assisted etching, respectively. The TAT and SAT were reproduced throughout the field evaporation and nitrogen field-assisted etching along the same crystal axis with its brightness 2.6 × 107 A/(m2 sr) and 1.6 × 108 A/(m2 sr), respectively. The field emission electron beam effective radii for three adatoms and single atom were calculated to be 2.90 Å and 1.47 Å, respectively, by Fowler-Nordheim plot, in which the single atom size was especially shown to be quite in good consistency with an atomic radius of tungsten.