Missing-row reconstruction in the system (2×1)O/Ag(110): A surface extended x-ray-absorption fine-structure study

Oxygen K-edge surface extended x-ray-absorption fine-structure studies on the (2×1)O/Ag(110) system confirm the long-bridge adsorption site with a nearest-neighbor O-Ag bond length of 2.05±0.03 Å. They show that oxygen adsorbs close to the surface inducing a reconstruction of the missing-row type. Structural similarities of the (2×1)O phases on Ni(110), Cu(110), and Ag(110) are discussed

Theoretical analysis of the electronic structure of the stable and metastable c(2x2) phases of Na on Al(001): Comparison with angle-resolved ultra-violet photoemission spectra

Using Kohn-Sham wave functions and their energy levels obtained by density-functional-theory total-energy calculations, the electronic structure of the two c(2x2) phases of Na on Al(001) are analysed; namely, the metastable hollow-site structure formed when adsorption takes place at low temperature, and the stable substitutional structure appearing when the substrate is heated thereafter above ca. 180K or when adsorption takes place at room temperature from the beginning. The experimentally obtained two-dimensional band structures of the surface states or resonances are well reproduced by the calculations. With the help of charge density maps it is found that in both phases, two pronounced bands appear as the result of a characteristic coupling between the valence-state band of a free c(2x2)-Na monolayer and the surface-state/resonance band of the Al surfaces; that is, the clean (001) surface for the metastable phase and the unstable, reconstructed "vacancy" structure for the stable phase. The higher-lying band, being Na-derived, remains metallic for the unstable phase, whereas it lies completely above the Fermi level for the stable phase, leading to the formation of a surface-state/resonance band-structure resembling the bulk band-structure of an ionic crystal.Comment: 11 pages, 11 postscript figures, published in Phys. Rev. B 57, 15251 (1998). Other related publications can be found at http://www.rz-berlin.mpg.de/th/paper.htm

High resolution NEXAFS studies of aromatic molecules adsorbed and condensed on Ni(111)

High resolution near-edge X-ray absorption fine structure measurements have been performed on benzene, pyridine and pyrazine adsorbed and condensed on Ni(111). The carbon K-edge multilayer data show the splitting of the e2u level of benzene into b1 and a2 levels for pyridine and into b3u and au levels for pyrazine; the corresponding π resonances are asymmetric due to the vibrational fine structure. At the nitrogen K-edge the transitions into the a2 and au levels are not observed. The benzene data suggest that the Rydberg orbitals are quenched in the condensed phase and that the broad structure above a photon energy of ∼300 eV is made up of (at least) two σ resonances. On adsorption the π resonances are considerably broadened at the adsorption edges of atoms which interact strongly with the substrate