Band Mapping in Higher-Energy X-Ray Photoemission: Phonon Effects and Comparison to One-Step Theory

In view of the present interest in more bulk sensitive band mapping via x-ray photoemission, we have studied the temperature dependence of W(110) angle-resolved spectra excited at photon energies of 260, 870 eV, and 1254 eV and between 300K and 780K. Experimental results are compared to both a free-electron final-state model and theoretical one-step model calculations. At 300K, clear band dispersions can be observed in the data. The ratio between direct and non-direct transitions is approximately estimated from a Debye-Waller factor. One-step theoretical calculations reproduce well band dispersions and matrix element effects in the measured spectra at room temperature, but including phonon effects via complex phase shifts does not predict density-of-states related features observed in higher-temperature spectra. We will also discuss the implications of this work for future experiments on other materials and at even higher photon energies up to 10 keV.