Band-structure effects in photofield emission.

Abstract

Photofield-emission energy distributions from W(110) and W(111) were measured using several photon energies in the range from 2.41 to 3.54 eV. The results are compared with theoretical expectations based on the electronic band structure of tungsten as well as calculations based on a free-electron model. A comparison between theory and experiment provides good evidence that initial-state bulk band-structure effects can explain small deviations in the W(110) photofield energy distributions from free-electron calculations. In contrast, for data taken from W(111), the experimental energy distributions provide little evidence for a gap in the band structure below ${E}_{F}$ along \ensuremath{\Gamma}P. A data-analysis technique is also described which reveals a photon-energy-dependent structure in the photofield energy distributions. A comparison of this structure to theoretical estimates of allowed bulk direct transitions reveals a correlation which indicates that bulk direct transitions, although small, are present in photofield-emission experiments.