| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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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| 6. |
- 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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| 7. |
- 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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| 8. |
- Ausmees, A., et al.
(författare)
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Secondary photoelectron spectra of ionic solids as a function of the incident photon energy
- 1991
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - 0168-9002. ; 308:1-2, s. 219-222
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Tidskriftsartikel (refereegranskat)abstract
- Energy distributions of slow electrons (0-10 eV) emitted by thin layers of NaCl, KBr, CsBr, and CsI irradiated by monochromatic XUV photons with various energies in the interval of 50-300 eV are measured. The contributions of slow secondaries, hot secondaries and primary photoelectrons are obtained. It is shown that the higher the absorption coefficient for incident photons, the stronger the contribution of hot secondaries. The relationship between their contribution and the electron-phonon scattering process is discussed.
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| 9. |
- Ausmees, A., et al.
(författare)
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Secondary photoelectron spectra of NaCl and KBr excited by XUV radiation : Experiments and computer simulations
- 1990
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Ingår i: Solid State Communications. - 0038-1098. ; 76:12, s. 1383-1386
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Tidskriftsartikel (refereegranskat)abstract
- Energy distributions of slow electrons (0 to 10eV) emitted by thin layers of NaCl and KBr irradiated by monochromatic XUV photons with various energies in the interval of 50 to 300 eV are measured. For all cases the photoelectron spectrum starts with an intense peak of slow secondaries and has a hot-secondary structure at the energies 1 to 5 eV. The smaller the photon absorption depth, the stronger is this structure. An attempt is made to reproduce such a behaviour of spectra by a Monte Carlo simulation of electron-electron and electron-phonon scattering sequences induced in solids by XUV photon absorption. It appears that for high-energy ( > 2 to 3 eV) conduction electrons the electron-phonon scattering is mainly due to acoustic phonons.
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| 10. |
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