Size effect in photofield emission from (0 0 1) tungsten

Photofield emission characteristics from (0 0 1) face of tungsten for p-polarized light are measured. By differentiation of the true photocurrent curves, after subtracting thermocurrents, energy distributions of electrons are determined. For different photon energies three groups of electrons are obtained and they fit well the maxima obtained theoretically. The regular spaced small maxima in each group treated as the final states, lie in the same energy range about 2 eV above the Fermi level and are interpreted as resonance states caused by the limited size of the microcrystal at the apex of the tungsten field emitter. Similar effect has been observed previously for a thin titanium microcrystal grown on a tungsten field emitter. This interpretation is supported here by model calculations of the density of states distributions at the surface region, performed for a one-dimensional semi-infinite system.