Atomic-scale field emitter with self-repairable function and thermodynamically stable structure: FEM study on Pd-covered nanopyramids on W<1 1 1> tips

We have fabricated nanometer-scaled pyramids on the W tip via Pd deposition and post-deposition annealing, and the field electron emission (FE) properties of the nanopyramids were investigated. Owing to the pyramid formation, the emission angles of the FE beams were drastically confined toward the forward direction. Further, the FE characteristics were reproduced via the self-repairing function inherently possessed by the nanopyramids. In the FEM observations, two characteristic features were seen. One is a rectangular triangle composed of three distinct spots, which is attributable to the trimer tip consisting of three atoms. The other pattern is a single bright spot, which is attributable to FE from a single atom tip. Semicone angle of the single-spot beam was 3.5°, which is comparable to those of the previous W nanotips.