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| Development of an approach extracting quantitative information regarding the atomic-layer and crystal-orientation resolved local structural relaxation, binding energy and the energetic behavior of electrons in a surface of skin depth from photoelectron emission has long been a great challenge though the surface-induced core level shifts of materials have been intensively investigated. Here we show that a combination of the bond order-length-strength (BOLS) correlation theory and the X-ray photoelectron spectroscope (XPS) has enabled us to derive information, from analyzing the 1s energy shift of Be(0001), (10 0), and (11 0) surfaces, for instance, regarding: (i) the energy levels of an isolated Be (1s: 106.40 eV) atom and its bulk shift (4.72 eV); (ii) the layer- and orientation-resolved effective atomic coordination, local strain, quantum trap depth, binding energy density and atomic cohesive energy of Be surface skins of four atomic layers in depth. It is affirmed that the broken-bond-induced local strain and quantum trapping perturb the Hamiltonian and hence the fascinating behavior of surface electrons. Developed approach can be applied to other systems containing high fraction of under-coordinated atoms such as adatoms, atomic defects and nanostructures to gain quantitative information and deeper understanding of the properties and processes due to coordination imperfection effect. |
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| Keywords:XPS;surface core level shift;binding energy |
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