Angle Resolved Ultraviolet Spectroscopy (ARUPS) brings the most direct information about the electronic structure of crystals, both for their bulk and for their surfaces. For a detailed interpretation of the energy distribution curves (EDC) of photoemitted electrons the one-step theory of photoemission is required. An adequate incorporation of final electron states appears necessary for elucidating of the surface sensitivity and of band mapping procedures. The resonant enhancement of the emission from surface states is explained by dipole transitions to evanescent components of final electron bands [1]. The oversimplifying schemes in the band mapping procedure have to be modified by taking into account the wave function of final states in order to adequately describe indirect transitions and interference effects in final states.
Normal photoemission from Al(111) and (100) surfaces induced by synchrotron radiation
is used together with the one-step ab initio theory for simultaneous description of surface and bulk features in the EDCs. Resonant enhancement of the surface state emission and its photon energy width are perfectly reproduced by the one-step theory. By fitting the line shape of the theoretical EDCs to the experiment the lifetime of the surface state is determined. Discrepancy in ‘experimental determining of the valence band width’ appears to be a consequence of not reaching the valence band minimum at Γ when tuning the photon energy in the band mapping. The often-neglected indirect transitions are shown to modify the EDCs below the Fermi level at several photon energies. Experimental observation of differences in the temperature dependence of bulk- and of surface- related peaks is discussed.
[1] E.E. Krasovskii, W. Schattke, Phys.Rev.Letters 93, 27601 (2004)
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