電界誘起酸素エッチングによるタングステン針の先鋭化と電子放出

抄録

A simple and repeatable modification technique for single-crystal tungsten <111> 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. 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 shape of the etched tip was evaluated by field evaporation and ball models. The sharpened tips emitted electrons at low-bias voltages with good geometrical confinement. The features of field emission were evaluated by Fowler-Nordheim plots. We are also developing a new method to obtain low-energy electron diffraction (LEED) patterns from surfaces using field emission beams. LEED patterns of the Cu(001) clean surface was observed using field-emitted electrons from tungsten tips. The typical emission current, bias voltage and estimated probing diameter for the observed diffraction patterns were 0.15 nA, 75 V, and 4 μm, respectively.