| 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. |
- Smedh, M., et al.
(författare)
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Vibrationally resolved C Is photoemission from CO absorbed on Rh(1 1 1) : The investigation of a new chemically shifted C Is component
- 2001
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Ingår i: Surface Science. - 0039-6028. ; 491:1-2, s. 99-114
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Tidskriftsartikel (refereegranskat)abstract
- High-resolution core-level photoemission at an energy resolution better than the intrinsic width of the C 1s level has been used to study the CO/Rh(1 1 1) overlayer system. C Is spectra have been measured in a large CO coverage range; from low coverages, where the CO molecules only adsorb in on-top positions, to saturation coverage, where CO molecules occupy both on-top and threefold hollow sites. Fine structure components due to vibrational excitation of the C-O stretch mode are clearly resolved in the emission peak from each site. The vibrational splittings and intensity ratios are found to be different for the different adsorption sites. A third C Is component, which has not been resolved earlier, is found at intermediate CO coverages. Some possible explanations for the origin of this extra component are discussed. In the light of its binding energy and vibrational energy in photoemission, together with supporting evidence from highresolution electron energy loss spectroscopy data and photoelectron diffraction, this is assigned to bridging CO species at intermediate coverages.
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| 3. |
- Nyholm, R., et al.
(författare)
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ELECTRONIC AND STRUCTURAL-PROPERTIES OF THE CU-BI2CASR2CU2O8 INTERFACE
- 1991
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Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 180:1-4, s. 120-123
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Tidskriftsartikel (refereegranskat)abstract
- The formation of the Cu-Bi2CaSr2Cu2O8 interface has been studied by photoelectron spectroscopy using synchrotron radiation. Photon energies in the range 20-1000 eV were utilized in order to probe both the valence band and to monitor chemical changes upon Cu deposition, as revealed by the core-level shifts. A strong chemical reaction between Bi2CaSr2CuO8 and Cu is manifested by the formation of metallic Bi. From the intensity variations as a function of electron emission angle it is shown that the metallic Bi segregates to the top surface layer.
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| 4. |
- Nyholm, R., et al.
(författare)
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SYNCHROTRON-RADIATION SOFT-X-RAY PHOTOEMISSION-STUDY OF LEAD ON BI2CASR2CU2O8
- 1992
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 46:10, s. 6488-6494
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present a study of the interaction of Pb with a clean single-crystal Bi2CaSr2Cu2O8 superconductor surface based on photoemission and low-energy electron diffraction (LEED). Deposition of Pb on a Bi2CaSr2Cu2O8 Crystal kept at room temperature gives rise to the formation of metallic Bi and oxidized Pb at the interface. This behavior could not be observed when the crystal was kept at 100 K during Pb deposition. For all investigated Pb overlayers on a cold crystal (100 K), surface-sensitive photoelectron spectroscopy revealed the growth of a covering metallic Pb overlayer film. The growth at 100 K, contrary to the growth at room temperature, preserved the original LEED 5 X 1 pattern even for Pb depositions corresponding to a 24-angstrom thick overlayer indicating epitaxial growth. Furthermore, a rigid 0.4-eV shift of the valence band and the Bi 5d core levels is observed upon initial Pb deposition and is tentatively attributed to electron doping.
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| 5. |
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| 6. |
- Andersen, J. N., et al.
(författare)
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Surface core-level shifts of some 4d-metal single-crystal surfaces : Experiments and ab initio calculations
- 1994
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Ingår i: Physical Review B (Condensed Matter). - 0163-1829. ; 50:23, s. 17525-17533
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Tidskriftsartikel (refereegranskat)abstract
- High resolution measurements are reported of the surface core-level shift of the 3d level for the Rh(111), Rh(110), Pd(111), Pd(110), and Ag(111) single-crystal surfaces. These measurements and earlier ones for the Mo(110), Rh(100), and Pd(100) surfaces are analyzed by ab initio calculations of the surface core-level shift. The calculations are found to reproduce well the trends of the experimental shifts with the 4d metal and with the crystal plane. The comparison between these experimental and theoretical results demonstrates the importance of proper inclusion of final-state effects for accurate calculations of surface core-level shifts. A core hole in a surface atom is found to be better screened than one in a bulk atom for the 4d metals to the left of Pd in the Periodic Table. The use of the Z+1 approximation to describe the core hole is investigated both by explicit use of this approximation and by performing calculations for 1s and 3d core holes, respectively. The Z+1 approximation is found to be well obeyed in the case of Ag whereas for the rest of the 4d transition metals it is less precise, introducing errors of typically 0.1 eV.
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| 7. |
- 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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| 8. |
- 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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| 9. |
- Smedh, M., et al.
(författare)
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Determination of the coverage dependent isosteric heat of adsorption of CO on Rh(1 1 1) by high resolution core level photoemission
- 2001
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Ingår i: Surface Science. - 0039-6028. ; 491:1-2, s. 115-123
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Tidskriftsartikel (refereegranskat)abstract
- High resolution core level photoemission is used to measure the equilibrium coverages of CO on Rh(1 1 1) at different sample temperatures and CO background pressures. Use of the chemical shifts of the C Is binding energy allows us to divide the total CO coverage into separate coverages for the different adsorption sites of CO on Rh(1 1 1). A Clausius-Clapeyron analysis of isosteres constructed from the measured isotherms for the total CO coverage is used to derive the coverage dependence of the isosteric heat of adsorption Eads for this adsorption system. The present results are found to agree well with a recent calculation of the adsorption energy for the Rh(1 1 1)-(2 × 2)-1CO structure at 0.25 ML (monolayer, ML). Furthermore, the present determination of Eads is consistent with a recent measurement of the zero coverage limit Eads(θ = θ ML) but is inconsistent with some previous determinations of this quantity. The coverage variation of the isosteric heat of adsorption is briefly discussed and put in relation to the relative occupations of different sites by the CO molecules.
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| 10. |
- Wigren, C., et al.
(författare)
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Sm- and Yb-induced reconstructions of the Si(111) surface
- 1993
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Ingår i: Physical Review B. - 0163-1829. ; 48:15, s. 11014-11019
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Tidskriftsartikel (refereegranskat)abstract
- Low-energy electron diffraction, scanning tunneling microscopy, and photoelectron spectroscopy results from the submonolayer Sm- and Yb-induced surface structures are presented. Several similar metal-induced surface reconstructions are found to exist for Yb and Sm on Si(111) for low submonolayer coverages: 3×2, 5×1, and 7×1. At higher submonolayer coverage, Yb induces a 2×1 reconstruction while Sm induces a (3 × 3) R30°-like reconstruction. Yb is found to be divalent in all structures, whereas the Sm valence increases with increasing coverage. In the 3×2 structure only divalent Sm is present, in the 5×1 and 7×1 structures a small amount of trivalent Sm appears, and, finally, in the (3 × 3) R30°structure approximately half of the Sm atoms are trivalent. The surface Fermi-level position in the band gap for the different Sm and Yb reconstructions has been measured. The difference in valence stability between Sm and Yb is suggested to be the cause of the difference in the high-coverage structures found and the differences in pinning level for the two elements observed for the 5×1 and 7×1 structures. © 1993 The American Physical Society.
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