Theory of Core-Level Shifts of Clean and Covered Surfaces
The core-level binding energy of an atom in the surface region is different from that of the bulk atoms1,2. From the measurement of this core-level shift many informations on the electronic states and surface properties can be devised. The interpretation of the surface core-level shift in terms of the one-electron picture is not a simple task, because the core-level binding energy (BE) is correctly viewed as an energy difference between the ground state and a core-hole final state of the system. This total energy difference, that determines the core-level BE, is not simply related to the single-particle eigenvalues, due to relaxation and correlation effects. For this reason single-particle eigenvalues are only a gross approximation to core-level BE. On the contrary the core-level BE shift, on going from the surface to the bulk environment, can be successfully related to the single-particle eigenvalue shift. We will show this for various surface systems: (i) a clean surface of a metal, Ni; (ii) an interface between a metallic monolayer and a semiconductor, Na-Si(111); (iii) a semiconductor- insulator interface, F-Ca-Si(111).
KeywordsCore Level Vacuum Region Empty Sphere Binding Energy Shift Atomic Sphere Approximation
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