Surface X-ray emission from lanthanide metals

O 3 X-ray emission (XE) upon 5p 3/2 electron-impact ionization of La(0 0 0 1) and Sm(0 0 0 1) metal surfaces exhibits up to 30% spectral intensity from the topmost atomic surface layer. The energy separation of surface and bulk XE peaks is explained by the surface core-level shift of La and the surface valence transition of Sm. While the bulk XE spectra are in reasonable agreement with theoretical sd partial density of states (DOS), the experimental access to the partial surface-layer DOS opens new opportunities in studying surface phenomena in lanthanide metals and compounds.