Microscopy and computational modelling to elucidate the enhancement factor for field electron emitters

We report on the computation of the electric field at the surface of single-tip field emitters for a variety of geometries and wide range of geometrical parameters. In conjunction with experimental work, this has allowed the determination of quantities useful for characterizing and comparing the performance of field emitters. The ratio of the field at the tip surface to field at a tip supporting base (enhancement factor) has been calculated for hemispherical tips with parallel or conical shanks, for ratios of tip length to tip radius from 1 to 3000. Enhancement factors greater than 1000 are achievable with suitable tip geometry. The threshold voltage dependence on the tip-anode separation for cylindrical tips facing a flat anode has also been calculated and reported.