Photoelectron photoemission matrix element

The various forms of photoelectron spectroscopy presently available permit a straightforward determination of occupied and unoccupied surface states. The most comprehensive and authoritative collection of reviews is in the book edited by Feuerbacher et al. [44], while Ertl and Kiippers [15] also provide useful information. Here, we will only attempt to summarize how the principal versions of the technique can be used in the determination of surface electronic structure. In this context the crucial factor is that photoemission spectra represent a direct manifestation of the initial and final density of states of the emitting system. Because selection rules (matrix element effects) can be involved in the transition, the state densities may not always correspond to those derived from the band structure, but in practice there is frequently a rather close correspondence. 

In the following it will be reported on a straightforward method to provide information about the dipole matrix elements and phase shifts being essential for the theoretical description of the photoemission process in a relatively simple way and with a pronounced accuracy [2]. This can be achieved by means of photoelectron spectroscopy with linearly polarized light using the ability of a continuous rotation of the electric field vector. The method is exemplarily demonstrated at the system hydrogen on Gd(0001)/W(l 10) which possesses a pronounced adsorbate induced state. 

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