Analysis of the electronic state of adsorbates on single crystals by angle-resolved photoelectron spectroscopy

A discussion of a few important novel aspects of the method is given. Ordered adsorbate layers are at present the main object of study by this technique. The physical conditions that dictate this limitation are discussed. It is shown that a detailed calculation of the matrix element of photoexcitation is still a difficult problem, so that those phenomena which do not depend directly on the value of matrix element are at the moment preferred to be studied. These are (1) symmetry, which is a simple but very useful information on adsorbate states obtained through selection rules, and (2) dispersion, which gives useful information about the electronic interaction among the adsorbate atoms themselves and between the adsorbates and substrate. The use of final-state resonance is shown to be an effective method of enhancing the emission from adsorbates.