Field-assisted oxygen etching for sharp field-emission tip

A simple and repeatable modification technique for single-crystal tungsten 〈1 1 1〉 oriented tips is reported. The modification technique was based on field-assisted oxygen etching of the peripheral tungsten atoms of the tip apex. Field-ion microscopy (FIM) was used to etch and to visualize the real-time etching events, and field emission patterns were observed at the same geometry. During modification via controlled etching of the tungsten tip, the FIM bias typically decreased from 4.4 kV to 1.6 kV. This bias change corresponded to a reduction of the radius of curvature from 10 nm to 3 nm. The sharpened tips emitted electrons at low- or extremely low-bias voltages with good geometrical confinement. The shape of the etched tip and the features of field emission were evaluated by field evaporation and Fowler-Nordheim plots.