| 1. |
- Nylén, H., et al.
(författare)
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O KVV Auger emission versus resonant photoemission at the O K edge of high-Tc superconductors
- 1998
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Ingår i: Physica C: Superconductivity and its Applications. - 0921-4534. ; 300:3-4, s. 161-170
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Tidskriftsartikel (refereegranskat)abstract
- Photoelectron spectroscopy results on single crystals of the superconductors Bi2Sr2CaCu2O8,Bi2Sr 2CuO6, Ba0.6K0.4BiO3 and the semiconductor Ba0.9K0.1BiO3 are reported for the photon energy region around the O K absorption threshold. The development of the O-KVV Auger structure has been carefully monitored as a function of photon energy. A non-monotonic behavior displaying a feature at a constant binding energy of about 14 eV was found for Bi2Sr2CaCu2O8 and Bi2Sr2CuO6 in a narrow photon energy region of 1 eV at the main edge of the O K absorption spectrum around 530 eV. The corresponding enhancement, connected with the autoionization of O 2 p states, is absent in Ba1-xKxBiO3 in contrast to Bi2Sr2CaCu2O8 and Bi2Sr2CuO6. The resonant enhancement is more pronounced for Bi2Sr2CuO6 as compared to Bi2Sr2CaCu2O8, which can be explained by a lower charge carrier concentration in the former case, leading to a more localized nature of intermediate O 2 p states. The model parameters Cu d-d and O p-p Coulomb interactions and the charge transfer energy Δ are estimated from the experiments.
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| 2. |
- Qvarford, M, et al.
(författare)
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Photoemission and x-ray absorption study of superconducting and semiconducting Ba1-xKxBiO3 single crystals
- 1996
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 54:9, s. 6700-6707
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Tidskriftsartikel (refereegranskat)abstract
- Semiconducting Ba0.9K0.1BiO3 and superconducting Ba0.6K0.4BiO3 single crystals cleaved in situ have been studied by core level and valence band photoelectron spectroscopy and O K edge x-ray absorption spectroscopy. It was found that the general shape of the valence band spectrum agrees with the shape predicted by band structure calculations, but the intensity near the Fermi level, was lower in the experimental spectrum as compared to the calculated. The O K edge spectra showed that the metallic phase is not related to the presence of doping inducted O 2p holes. This property of Ba1-xKxBiO3 shows that the semiconductor-metal transition of this system is of a different nature than that of the hole doped cuprate high-T-c superconductors. The core level photoemission spectra of the cations showed a small asymmetry for Ba0.9K0.1BiO3. Corresponding spectra for Ba0.6K0.4BiO3 showed a larger asymmetry resulting in a resolved high binding energy shoulder in the Bi 4f spectrum. The origin of this feature is discussed.
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| 3. |
- Ruus, R., et al.
(författare)
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M4,5N4,5N4,5 Auger decay spectra of the resonantly excited 3d94f configuration of xenonlike ions in solids
- 1994
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Ingår i: Physical Review B (Condensed Matter). - 0163-1829. ; 49:21, s. 14836-14844
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Tidskriftsartikel (refereegranskat)abstract
- The synchrotron-radiation-induced Auger and photoelectron spectra of the xenonlike ions I- (in CsI), Cs+ (in CsI), Ba2+ (in BaF2), and La3+ (in LaF3) have been measured in the vicinity of the M4,5 absorption edges of these ions. It is shown that the spectra of La and Ba measured at 3d10→3d94f resonances exhibit a very intense 4f-spectator structure which changes its energy and intensity with the energy of the exciting photons. Calculation of the Auger decay of the 3d-14f configuration shows that this structure is due to transitions to the 4d-24f+4p-1 final ionic configuration, the high-energy part of which overlaps the 4d-2 continuum. In the case of Ba this structure coexists with the normal Auger structure which appears as a result of the M4M5N6,7 Coster-Kronig transitions. The spectra of I- contain only the normal M4,5N4,5N4,5 Auger structure related to the 3d-1→4d-2 transitions. The spectra of Cs+ are similar to those of I- with a small admixture of the 4f-spectator-like structure.
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| 4. |
- Zakharov, A. A., et al.
(författare)
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Metal-dielectric transition in Ba0.6K0.4BiO3-y single crystals studied by scanning photoelectron microscopy
- 1997
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Ingår i: Physical Review B (Condensed Matter). - 0163-1829. ; 56:10
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of Ba0.6K0.4BiO3-y single crystals has been studied using a scanning photoelectron microscope with a lateral resolution in the one micrometer range. It is possible to change the oxygen content (y) and convert the surface from the metallic to the dielectric state presumably by breaking the Bi-O bonds by using the focused zero-order light to irradiate the sample surface. The electronic states close to the Fermi level after such a treatment show a different doping dependence as compared to the case of potassium doping. By imaging the surface on the micrometer scale we find significant variations in the valence band intensity over the surface and observe a rather large intensity of the density of states close to the Fermi level. This will have a large impact on the discussions of dynamical lattice distortion and pseudogap behavior in the metallic phase.
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| 5. |
- Andersen, J. N., et al.
(författare)
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Alkali metal adsorption on Al(111)
- 1993
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 289:3, s. 307-334
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Tidskriftsartikel (refereegranskat)abstract
- The submonolayer adsorption of Na, K, Rb, and Cs on the Al(111) surface at 100 K and at room temperature is investigated by high resolution core level spectroscopy and low energy electron diffraction. It is found that the first alkali atoms on the surface adsorb at surface defects. At higher coverages, up to approximately one third of the maximum submonolayer coverage, alkali atoms adsorbed at defects coexist with a dispersed phase. At higher coverages island formation is found to occur for the majority of the systems. It is argued that all of the ordered structures formed at room temperature involve a disruption of the Al(111) surface in contrast to the situation at 100 K where the alkali atoms adsorb as adatoms.
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| 6. |
- Andersen, J. N., et al.
(författare)
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Changes in the local surface geometry with conserved adsorbate coverage and long-range order caused by annealing
- 1992
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Ingår i: Physical Review B (Condensed Matter). - 0163-1829. ; 46:19, s. 12784-12787
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Tidskriftsartikel (refereegranskat)abstract
- The ordered c(2×2) Na on Al(100) and (3 × 3) R30°K on Al(111) structures formed at either 100 K or at room temperature are studied by high-resolution core-level spectroscopy. For both systems equal alkali coverages are found at these two temperatures. The core-level spectra, however, show strong changes with temperature. This behavior leads to the surprising conclusion that annealing at room temperature causes an irreversible change in the local geometry, i.e., of the adsorption site, of the overlayer even though neither the long-range order nor the adsorbate coverage changes.
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| 7. |
- Andersen, J. N., et al.
(författare)
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Intermixing in the Na on Al(111) system
- 1992
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Ingår i: Physical Review Letters. - 0031-9007. ; 68:1, s. 94-97
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Tidskriftsartikel (refereegranskat)abstract
- Ordered structures formed by Na adsorption on the Al(111) surface are investigated by high-resolution core-level spectroscopy. It is shown that, contrary to the common picture of alkali adsorption, two of the structures formed at room temperature consist of intermixed Na-Al layers. The results for the (3 ×)-rotated-30°structure are also consistent with intermixing although they do not provide any definite proof. For Na layers deposited at 100 K no intermixing is found.
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| 8. |
- Andersen, J. N., et al.
(författare)
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Surface core-level shifts as a probe of the local overlayer structure : CO on Pd(100)
- 1991
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Ingår i: Physical Review Letters. - 0031-9007. ; 67:20, s. 2822-2825
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Tidskriftsartikel (refereegranskat)abstract
- The bonding energies of the Pd 3d and the C 1s core levels have been studied for the p(2 S 2 × 2) R45°, p(3 s2 × S2) R45°, and p(4 S 2 × S 2) R45°structures of CO on Pd(100). Adsorption of CO shifts the Pd 3d surface emission to higher binding energies with the magnitude of the shift depending almost linearly on the number of Pd to CO bonds; the measured shift per bond is close to 0.5 eV. A direct relation is established between the detailed geometry of the CO overlayer and the changes in the Pd 3d spectra.
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| 9. |
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| 10. |
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