Directional photoemission from tungsten

Abstract

Photoemission energy distribution spectra have been scanned for photoelectrons emitted normal to two different crystal faces of tungsten, namely (100) and (110). The energy distributions and the derivative spectra show large differences between emission from the two faces. Whereas strong surface state emission is observed from the (100) face, no surface states are associated with the (110) face. The spectra show features characteristic of direct and also nondirect transitions, but these features appear very different for the two faces. Using existing band structure calculations, the spectral structure is assigned to electronic transitions between bands along the Δ axis for the (100) face and the Σ axis for the (110) face. The experiments show that directional photoemission spectra taken normal to a crystal surface make it possible to investigate electronic energy bands along symmetry directions in the Brillouin zone.