Abstract
The (110) surface of a perovskite sodium tungsten bronze with composition close to Na 2/3 WO 3 has been studied by X-ray and ultraviolet photoemission spectroscopy (XPS and UPS), electron-energy-loss spectroscopy (EELS) and low-energy electron diffraction (LEED). The chemical composition at the surface differs little from that in the bulk, but sodium ion ordering along the [1̄10] direction leads to a (3 × 1) superstructure not evident in bulk diffraction experiments. The UPS data give no indication of surface electronic states in the bulk bandgap, although a surface plasmon loss peak is seen. By contrast fine structure in the tungsten 4f region does not arise from plasmon excitation and must be ascribed to final state screening effects. The screening mechanism is discussed in relation to the UV photoemission spectra.
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