| 1. |
- Qvarford, M., et al.
(författare)
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Polarisation-dependent X-ray absorption in high- and low-Tc Bi2Sr2Can-1CunO4+2n superconductors
- 1993
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Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 214:1-2, s. 119-126
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Tidskriftsartikel (refereegranskat)abstract
- Taking advantage of the linear polarisation of synchrotron radiation, the polarisation dependence of the O K and Cu L3 X-ray absorption edges has been compared for in situ cleaved Bi2Sr2CaCu2O8 and Bi2Sr2CuO6 single crystals. The X-ray absorption spectra were measured by means of total electron yield detection. The spectra show for both crystals that the lowest unoccupied Cu 3d and O 2p orbitals are dominantly oriented parallel to the a-b plane, but also the presence of a small amount of unoccupied orbitals oriented perpendicular to the a-b plane can be deduced from both the O K and Cu L3 absorption spectra. A shift of the order of 0.5 eV between absorption into the in-plane and the out-of-plane Cu 3d orbitals was measured for the Bi2Sr2CaCu2O8 crystal, but no such shift was found for the Bi2Sr2CuO6 crystal.
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| 2. |
- 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
-
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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| 3. |
- Berg, C., et al.
(författare)
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Observation of a low-binding-energy peak in the 2p core-level photoemission from oxidized Al(111)
- 1993
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Ingår i: Physical Review B (Condensed Matter). - 0163-1829. ; 47:19, s. 13063-13066
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Tidskriftsartikel (refereegranskat)abstract
- High-resolution photoemission studies of oxidation of the Al(111) surface have been performed. The appearance of a component at lower binding energy than the metallic bulk Al emission in the Al 2p spectrum at oxygen exposures above ∼50 langmuir (1 L = 10-6 Torr s) is argued to be due to Al atoms which do not bond directly to oxygen atoms at the oxide-metal interface. Low-energy electron diffraction initially shows a 1×1 structure, which subsequently fades away at higher oxygen exposures, 400 L.
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| 4. |
- 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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| 5. |
- 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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| 6. |
- QVARFORD, M, et al.
(författare)
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X-RAY-ABSORPTION AND RESONANT-PHOTOEMISSION STUDY OF CA IN THE HIGH-TEMPERATURE SUPERCONDUCTOR BI2SR2CACU2O8
- 1992
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 46:21, s. 14126-14133
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of Ca in the high-temperature superconductor Bi2Sr2CaCu2O8 has been studied by x-ray-absorption spectroscopy and resonant-photoemission at the Ca L2,3 absorption edge. In the x-ray-absorption spectrum no edge structure is seen at the energy corresponding to the Ca 2p3/2 core-level binding energy, in agreement with the very low Ca density of states at the Fermi level predicted by band-structure calculations. Furthermore, the crystal-field splitting of the Ca 3d level, which is characteristic of ionic Ca compounds, is clearly observed in the x-ray-absorption spectrum. The photoemission spectra display strong resonant enhancements of the Ca 3s and 3p core levels as well as strong changes in the intensity and the line shape of the Ca L2,3M2,3M2,3 Auger structure at the Ca L2,3 threshold, showing the localized nature of the 3d states in core ionized Ca. The 3d induced spectator shift of the Ca L2,3M2,3M2,3 complex is fairly small as compared to what has been reported for CaF2, indicating that the screening of the normal Auger final state by the charge carriers in the surrounding Cu-O2 layers is quite efficient. From the Ca L2,3M2,3M2,3 data it is also suggested that, at the Ca L2 threshold, the excited 3d electron participates in a Coster-Kronig-type decay resulting in a 2p3/2 core hole followed by a normal L3M2,3M2,3 Auger decay.
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