Electronic resonances in the photofield emission spectra from Ta(1 1 1)

Abstract

The energy distributions of photoelectrons obtained from field emission spectroscopy performed for Ta(111) indicate the presence of the fine structure of peaks separated by a few hundredths of an electron volt. New experimental data show also that these peaks appear practically for the same energies in the spectra of both the surface region and the bulk of the field emitter. Our theoretical study performed with the help of the simple one-dimensional model shows that this effect might be a result of the partial reflection of the electronic waves between the Schottky barrier and a border separating the topmost part of the field emitter from the rest of the tip. This mechanism may lead to the formation of the electronic resonance states in the apex part of field emitter, which is manifested in the photofield emission spectra by the fine structure of peaks. We have studied the influence of the changes of the morphology of the tip, caused by the annealing process, on the energy separation between the nearest peaks: experimental results and numerical computations give an additional support for the supposition that the observed dense structure of peaks represents electronic resonances existing in the topmost part of the field emitter.