ABSTRACT Appearance potential spectroscopy is a surface sensitive technique and provides information about the unoccupied density of states above the Fermi level. In this technique, the sample is bombarded with monoenergetic electrons and the x-ray or secondary electron yield is monitored. The signal is extracted from the large background using a potential modulation technique. The signal strength is proportional to the density of states at the Fermi level. Therefore, this technique is suitable to study the transition metals, the rare earths, and their intermetallics. It reveals a localized density of states because the matrix element governing the core hole production involves the very short range wave function of the initial core electron states. It reveals information regarding the total density of states of all symmetries in the conduction band. Since the density of states above EF correlate with the number and not with the energy, APS does not require energy analysis of the products of the experiment. It is, therefore, termed as a nondispersive spectroscopy. This accounts for the extreme simplicity of the APS spectrometer. In this article, the usefulness of this technique in elucidating the electronic structure of rare earth-transition metal intermetallics is discussed.
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