Angle-resolved photoemission determination of the band structure of Ru(001)

Synchrotron radiation in the energy range from 11 to 80 eV has been used to identify critical points in the Ru band structure along 〈001〉 and to map the energies of the electronic states. The experimental band structure is compared to various theoretical calculations. We find good agreement between experiment and calculations using the proper hcp symmetry for the occupied bands. Peaks in the photoemission spectra not related to direct bulk transitions are attributed to surface states or resonances (i.e., a part of the peak in the vicinity of EF and a peak at EB=-5.6 eV), and to two-electron excitations (at a binding energy EB of {}-7.3 eV, in coincidence with a one-electron band-structure state) which are resonantly enhanced at the Ru 4p core level. Another prominent peak in the spectra at fixed kinetic energy of {}16.5 eV relative to EF must be attributed to emission into a flat final band. The interpretations are supported by theoretical calculations of the photoemission intensities. The calculations are based on the one-step model of the photoemission process.