Angle-resolved x-ray photoemission from the valence bands of tungsten with high angular resolution and temperature variation

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Abstract
Angle-resolved valence photoemission spectra have been obtained for W(011) and W(001) using Al Kα and Mg Kα excitation and with both normal and off-normal emission directions. The angular resolution was ≲±1.0°, and thus the highest to date in this energy regime, and the temperature also was varied from 295 to 1000 K. These spectra exhibit features very strongly dependent on emission direction and temperature that can be more precisely associated with direct-transition emission from different Brillouin-zone points than in prior studies. Data obtained at different temperatures are used to deconvolute direct- and nondirect-transition components. The direct-transition components are found to include residual intensity due to nondirect transitions. The simple direct-transition model applied previously to the analysis of such data is also extended to include the effects of correlated lattice vibrations via a cylindrical broadening in k space. This model is found to describe semiquantitatively the effects of phonon-assisted nondirect transitions on spectra.