Introduction

In this chapter we present photoelectron spectra of several materials. We present valence-band data for all of them, and in most cases core-level spectra are discussed. Na is a simple metal, about as simple a metal there is. If the photoelectron spectra of Na cannot be understood it is difficult to be comfortable with interpretations of photoelectron spectra of the cuprates. Cu and Ni are more complicated, having 3d bands near and spanning the Fermi level, respectively. Then we present results on NiO, Cu2O, and CuO which introduce new effects. The photoelectron spectra of NiO and especially CuO bear some resemblance to those of the cuprates. The studies reported on the three oxides do not represent all of the work on these materials. Studies on related materials, e.g., Cu- and Ni halides, have been useful, for one can see the influence on the photoelectron spectra of changes in ionicity, number, type, and disposition of nearest neighbors, and distances between nearest neighbor transition metal atoms. Studies of a series of 3d transition-metal oxides are also helpful, but we do not discuss these here. Another approach, also not discussed here, is to start with a clean single-crystal surface of a transition metal and let it oxidize in stages in the experimental chamber, taking spectra and LEED patterns at various stages. In some cases, e.g., NiO, the final stage may be several layers of the same oxide that is studied in bulk samples.