Abstract
The fine structure of the Ca 2p soft-x-ray-absorption edge is studied for a variety of bulk compounds (Ca metal, , CaO, and ), for surfaces and interfaces [(111), on (111), Ca and on Si(111)], and for defects (F centers in ). The observed multiplet structure is explained by atomic calculations in a crystal field [cubic for the bulk and threefold for the (111) surfaces and interfaces]. While the bulk spectra are isotropic, the surface and interface spectra exhibit a pronounced polarization dependence, which is borne out by the calculations. This effect can be used to become surface and/or interface selective via polarization-modulation experiments, even for buried interfaces. A change in valence from to causes a downwards energy shift and extra multiplet lines according to the calculation. The energy shift is observed for F centers at the surface and for the /Si(111) interface.
- Received 15 October 1990
DOI:https://doi.org/10.1103/PhysRevB.43.6899
©1991 American Physical Society