| 1. |
- Andersen, Jesper N., et al.
(författare)
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Core level binding energy shifts in interfaces between 4d and alkali metals
- 1995
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048. ; 75:C, s. 225-232
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Tidskriftsartikel (refereegranskat)abstract
- High resolution core level photoemission measurements are reported of the binding energy shifts of the 3d core level of Mo, Rh and Pd atoms in interfaces between these 4d metals and alkali metals. The core level binding energies of the interface 4d atoms are found to be almost equal to those of the clean surface atoms for Mo and Rh. For Pd a large alkali induced shift towards higher binding energy is found. The implications of these results for the information derivable from core level binding energy shifts in metallic interfaces are discussed and it is demonstrated that the present results are explained by established total energy based models for core level binding energy shifts in metallic systems.
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| 2. |
- Bässler, M., et al.
(författare)
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Soft x-ray undulator beam line 1411 at MAX-II for gases, liquids and solid samples
- 1999
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048. ; 101-103, s. 953-957
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Tidskriftsartikel (refereegranskat)abstract
- We report on the build-up of the new undulator beam line 1411 at the third-generation synchrotron radiation facility MAX II in Lund, Sweden. This beam line is based on an upgraded version of the modified SX700-monochromator and the end station which were installed previously at beam line 51 at MAX I. The end station is equipped with a rotatable Scienta hemispherical electron-analyser making angle-resolved high resolution electron spectroscopy possible for various kinds of samples. The beam line performance will be considerably improved on MAX II due to a new undulator and the superior light source properties, e.g. the small vertical electron beam size. Undulator spectra have been measured and estimates of the photon flux at the experiment and the expected energy resolution are presented. The parameters for a new refocusing mirror were defined by ray tracing using the beam waist of the undulator. The beam line length was extended by 1 m to offer additional space for exchangeable experimental chambers.
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| 3. |
- Denecke, R., et al.
(författare)
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Beamline 1511 at MAX II, capabilities and performance
- 1999
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - 0368-2048. ; 101-103, s. 971-977
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Tidskriftsartikel (refereegranskat)abstract
- The new undulator beamline 1511 at MAX-lab, now under commissioning, has been optimized for X-ray emission and photoelectron spectroscopies. Using an SX-700 high flux monochromator the accessible photon energy range is from 90 eV to about 1500 eV. The performance of the undulator agrees very well with the specifications, as shown by measurements using a photodiode. The energy resolution of the monochromator has been checked using absorption measurements in a gas cell. It was found to meet the expectations and exceeds a resolving power of 10 000 at 244 eV. The photon flux as a function of energy has been recorded as well and gives a maximum flux of 3×1013 photons/s/100 mA/0.1% BW. Beamlines 1511 and 1411 will be the first synchrotron beamlines making use of a so-called beam waist phenomenon, known from laser physics. We show results of ray-tracing calculations to determine the ultimate spot size on the sample location. The endstations to be used at this new beamline and their capabilities will be discussed as an example of the future use of this facility.
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| 4. |
- Fujikawa, Takashi, et al.
(författare)
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A self-consistent optical potential theory for atoms in solids
- 1998
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - 0368-2048. ; 88-91, s. 649-655
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Tidskriftsartikel (refereegranskat)abstract
- We develop an approximation for the optical potential in a solid, valid at intermediate energies, i.e. energies greater than 50 eV. The present approximation for the optical potential builds on the GW-expression. We separate the RPA polarization propagator into a core electron and a valence electron, and can then achieve a corresponding separation of the optical potential. We apply this method to electron-Ne and -Ar elastic scatterings and find a satisfactory agreement with the observed results. We also study the importance of self-consistency and the sensitivity to a parameter, the average excitation energy.
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| 5. |
- Hedin, Lars
(författare)
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Optical potentials and damped one-electron functions in photoemission and electron scattering
- 1990
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - 0368-2048. ; 51, s. 91-102
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Tidskriftsartikel (refereegranskat)abstract
- Recently a new approach to photoemission, EXAFS and electron scattering has been developed. The correlations between target electrons are separated from the active electron-target electron correlations, and the damping effects are coming out explicitly. The theory uses van Hove diagonal Green's functions and projection operator techniques, not the usual diagram expansions. By omitting from the start terms in the Hamiltonian which lead to reabsorption of the active electron (photoelectron or scattered electron), remarkably simple expressions are obtained. These expressions contain optical potentials which damp the electron propagation, and “fluctuation potentials” which determine the inelastic scattering. The fluctuation potentials also appear in the expressions for the optical potentials. On the RPA level of approximation the fluctuation potentials are obtained from the dielectric response function of the target. The theory is quite general, but its main advantages are for extended systems, where the damped propagators and damped one electron functions are important effects. The present theory should make it possible to quantitatively attack a number of correlation effects in different spectroscopies.
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| 6. |
- Hedin, Lars, et al.
(författare)
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Sudden approximation in photoemission and beyond
- 2002
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - 0368-2048. ; 124:2-3, s. 289-315
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Tidskriftsartikel (refereegranskat)abstract
- The conditions behind sudden approximation are critically examined. The fuzzy band expression is derived in detail from first principles. We go beyond the sudden approximation to account for both extrinsic losses and interference effects. In an extension of earlier work we discuss both core and valence satellites including both intrinsic and extrinsic amplitudes, and high energy excitations as well as low energy electron-hole pairs. We show how the extrinsic losses in photoemission can be connected with the electron energy loss function. This is achieved by three approximations, to connect the dynamically screened potential in the bulk solid to the loss function, to account for the surface, and lastly to extrapolate zero momentum loss data to include dispersion. The extrinsic losses are found to be weak for small loss energies. For larger loss energies the extrinsic losses can be strong and have strong interference with the intrinsic losses depending on the nature of the solid. The transition from the adiabatic to the sudden regime is discussed for atoms and localized systems and compared with the situation for solids. We argue that in solids for photoelectron energies above some 10 eV the external losses are mainly connected with spacially extended excitations. We discuss strongly correlated quasi-two-dimensional solids with Bi2212 as example, and find an asymmetric broadening of the main peak from shake up of acoustic three-dimensional plasmons. In the superconducting state the loss function is assumed to have a gap, which then leads to a peak-dip-hump structure in the photoemission spectrum. This structure is compared with a corresponding structure in tunneling. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 7. |
- Johansson, U., et al.
(författare)
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Thermal desorption of oxides on Si(100) : A case study for the scanning photoelectron microscope at Max-Lab
- 1997
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - 0368-2048. ; 84:1-3, s. 45-52
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Tidskriftsartikel (refereegranskat)abstract
- A scanning photoelectron microscope, utilizing a focused beam of monochromatized photons in the energy range from 15 to 150 eV, has been used to study the thermal desorption of oxide layers on Si(100). The instrument can provide high-resolution photoelectron spectra from selected parts of the surface as well as images showing the lateral distribution (on a micrometer scale) of elements in different chemical states by monitoring the photoemission intensity of chemically shifted core levels. Both native (10-15 Å) and thick (200-400 Å) oxides have been studied. The desorption (at 840°C) of the native oxide proceeds through a phase of irregular (on a micrometer scale) and diminishing areas of dioxide until a clean surface is obtained. For the thick oxide, annealing to 1100°C creates circular voids in the oxide layer which grow linearly in diameter with annealing time. The surface in these voids mainly consists of clean silicon but a small amount of remaining SiO2 is observed. This remaining dioxide most probably consists of small clusters or particles. For both types of oxide, we find, during and after desorption, a surface-shifted component in the Si 2p core level spectra indicating that at least parts of the surface have an ordered structure which most probably is a 2 × 1 reconstruction.
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| 8. |
- Zakharov, Alexei, et al.
(författare)
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Anisotropy of the electronic structure of low-dimensional Sr(Ca)CuO2 single crystals studied by scanning photoelectron spectromicroscopy
- 2002
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - 0368-2048. ; 122:3, s. 203-208
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Tidskriftsartikel (refereegranskat)abstract
- The energy band structure of superconducting (T-c(onset) = 80 K), low-dimensional Sr(Ca)CuO2 single crystals was studied by photoelectron spectromicroscopy. The sample consists of double parallel Cu-O chains, and spectra show a strong anisotropy for electron momenta k parallel and perpendicular to the chain direction q. Spectra were collected with two experimental setups: kparallel toq (Aperpendicular toq) and kperpendicular toq (Aparallel toq), where A is the electric field vector of the incident photon beam. By imaging the surface on the micrometer scale we find significant variations in the valence band intensity in the vicinity of about 2 eV below the Fermi level for kparallel toq. For this geometry, Aperpendicular toq and the spectra are very sensitive to beam damage. This effect can be related to the breaking of weak inter-chain bonds with the high flux density (similar to10(18) photons s(-1) cm(-2)) beam focused on the sample surface.
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| 9. |
- Butorin, S. M., et al.
(författare)
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Resonant inelastic soft X-ray scattering at the 4d edge of Ce-based heavy fermion materials
- 1999
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - 0368-2048 .- 1873-2526. ; 101-103, s. 783-786
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Tidskriftsartikel (refereegranskat)abstract
- Resonant X-ray scattering measurements were performed on CeB6, CeAl, γ-Ce, and α-Ce at various incident-photon energies near the Ce 4d threshold. A pronounced inelastic scattering structure which has 4f character is observed at about 4 eV below the elastic peak. The structure shows a distinct resonant behavior as well as a dependence on the degree of 4f hybridization and can therefore be attributed to charge-transfer excitations to the 4f0 state. The intensity of the elastic peak increases when going from the systems with low Kondo temperature TK to those with high TK which is consistent with a Kondo scale behavior. By analyzing the scattering data, a controversial issue on the validity of a single-impurity Anderson model in heavy-fermion materials is addressed.
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| 10. |
- CHAKAROV, DV, et al.
(författare)
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INTERACTION OF WATER WITH POTASSIUM ON GRAPHITE - A HREELS STUDY
- 1993
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 64-5, s. 279-285
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Tidskriftsartikel (refereegranskat)abstract
- Water and coadsorbed water + potassium on the basal plane of graphite were studied with high resolution electron energy loss spectroscopy (HREELS) at 85 K and after stepwise annealing up to 500 K. Water adsorbs non-dissociatively on both clean and potassium precovered surface at 85 K. The vibration spectra, together with thermal desorption spectroscopy (TDS) reveal a series of reactions within the coadsorbed layer leading to the formation of KOH, KH, and KOx and volatile products. Eventually a precursor to CO2 formation, of yet unindentified composition and observed also in K + O-2 coadsorption studies on graphite, is observed at approximate to 27 meV.
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