| 1. |
- Vos, M., et al.
(författare)
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Determination of the energy-momentum densities of aluminium by electron momentum spectroscopy
- 1999
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Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 11:18, s. 3645-3661
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Tidskriftsartikel (refereegranskat)abstract
- The energy-resolved momentum densities of thin polycrystalline aluminium films have been measured using electron momentum spectroscopy (EMS), for both the valence band and the outer core levels. The spectrometer used for these measurements has energy and momentum resolutions of around 1.0 eV and 0.15 atomic units, respectively. These measurements should, in principle, describe the electronic structure of the film very quantitatively, i.e. the dispersion and the intensity can be compared directly with theoretical spectral momentum densities for both the valence band and the outer core levels. Multiple scattering is found to hamper the interpretation somewhat. The core-level intensity distribution was studied with the main purpose of setting upper bounds on these multiple-scattering effects. Using this information we wish to obtain a full understanding of the valence band spectra using different theoretical models of the spectral function. These theoretical models differ significantly and only the cumulant expansion calculation that takes the crystal lattice into account seems to describe the data reasonably well.
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| 2. |
- Nilsson, P. O., et al.
(författare)
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Electronic structure of buried Si layers in GaAs(001) as studied by soft-x-ray emission
- 1995
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 52, s. R8643-
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Tidskriftsartikel (refereegranskat)abstract
- It is demonstrated that it is possible to investigate details of the electronic structure of an internal atomic monolayer using soft-x-ray-emission spectroscopy. The local and partial density of states of one monolayer and three monolayers of Si, embedded deep below a GaAs(001) surface, was extracted. Clear differences to the density of states for bulk Si were observed.
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| 3. |
- Rensmo, Håkan
(författare)
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Dye-sensitized nanostructured metal oxide electrodes : Photoelectrochemical, quantum chemical and electron spectroscopic studies
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Solar cells based on dye-Sensitized nanostructured electrodes are promising for solar energy conversion. High overall light-to-energy conversion efficiencies have been obtained for systems based on TiO2 (7%) and ZnO (2%). The photocurrent losses in these electrodes have been investigated by photoelectrochemical methods. Both bare and dye-sensitized TiO2 and ZnO electrodes were studied. The measurments showed that the losses in photon to current conversion efficiency were largely dependent on the electrolyte composition and penetration depth of the light. Generally the probability of losing generated charges decreased with increased travelling distancees within the nanostructured film and with the increased concentration of electron scavengers within the electrolyte.Ruthenium polypyridine complexes are presently used as light absorbers in the dye-sensitized solar cell. The electronic structure of these dyes, and of the dyes adsorbed to nanostructured TiO2 surface was investigated by means of semiempirical quantum chemical calculations and photoelectron spectroscopy. The investigation gave insight into the electronic structure involved in the light-to-energy conversion process. To date the most efficient dyes contain bi-isonicotinic acid as attaching ligand to the nanostructured surface. A semiempirical and electron spectroscopic investigation of this ligand attached to the TiO2 rutile (110) surface was performed to investigate the molecular structure at the surface. An adsorption configuration with four equivalent oxygen bridges was proposed.
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| 4. |
- Magnuson, Martin, et al.
(författare)
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Competition between decay and dissociation of core-excited carbonyl sulfide studied by x-ray scattering
- 1999
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 59:6, s. 4281-4287
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Tidskriftsartikel (refereegranskat)abstract
- We show evidence of dissociation during resonant inelastic soft x-ray scattering Carbon and oxygen K-shell and sulfur L-shell resonant and nonresonant x-ray emission spectra were measured using monochromatic synchrotron radiation for excitation and ionization. After sulfur L-2,L-3-->pi*, sigma* excitation, atomic lines are observed in the emission spectra as a consequence of competition between de-excitation and dissociation. In contrast thr carbon and oxygen spectra show weaker line-shape variations and no atomic Lines. The spectra are compared to results from ab initio calculations. The discussion of the dissociation paths is based on calculated potential energy surfaces and atomic transition energies.
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| 5. |
- Hamamoto, Ikuko, et al.
(författare)
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Form-factor of low-lying Kπ=1+ excitations in rare-earth nuclei
- 1987
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693. ; 194:1, s. 6-10
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Tidskriftsartikel (refereegranskat)abstract
- The differential cross section of inelastic electron scattering for the low-lying “collective” Kπ=1+ excitations in rare-earth nuclei is calculated in DWBA by using microscopically calculated transition-densities. In the region of low-momentum transfer (q⪅0.5 fm-1) in which experimental data are available the shape of calcualted cross sections is almost the same for all nuclei and is slightly but systematically different from the observed shape.
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| 6. |
- Chu, H.S., et al.
(författare)
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VLBI observations of the puzzling BL Lacertae object 0235+164
- 1996
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Ingår i: Astronomy and Astrophysics. - : Springer. - 0004-6361 .- 1432-0746. ; 307:1, s. 15-20
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Tidskriftsartikel (refereegranskat)abstract
- For over 20 years, many models have been proposed to explain the variability of AO0235+164. Among them, the most favorable has been micro-lensing. We have made a series of VLBI observations on this source in order to better understand its nature. The resultant maps indicate dramatic changes in the position angle of the jet between observations as well as a correlation between the intensity of the VLBI core and flux outbursts which occurred between the observing sessions. These characteristics, in conjunction with other arguments, suggest that the source variability is intrinsic, i.e. microlensing is of minor importance. We suggest two models: 1) a model in which the jet starts at a very small angle to the line of sight and then curves away to become about 6deg at about 1 mas from the core; and 2) a CME (Coronal Mass Ejection) model that also may explain the violent variability in intensity, polarization position angle, and jet direction in AO0235+164.
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| 7. |
- Magnuson, M., et al.
(författare)
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Angular-dependent resonant-photoemission processes at the 2p thresholds in nickel metal
- 1999
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 60:4, s. 2436-2440
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Tidskriftsartikel (refereegranskat)abstract
- Angle-resolved valence-band resonant-photoemission of nickel metal has been measured close to the 2p core-level thresholds with synchrotron radiation. The well-known 6-eV correlation satellite has an intensity enhancement of about two orders of magnitude at resonance. The angular dependence of the photoemission intensity has been studied as function of photon energy and provides unambiguous evidence for interference effects all the way up to the resonance maximum. The observation of different angular asymmetries, β, for the valence band and the satellite is discussed in connection to the origin of the resonant-photoemission process and the character of the satellite.
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| 8. |
- Magnuson, Martin, et al.
(författare)
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Energy dependence of Cu L2,3 satellites using synchrotron excited x-ray-emission spectroscopy
- 1997
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 56:19, s. 12238-12242
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Tidskriftsartikel (refereegranskat)abstract
- The L2,3 x-ray emission of Cu metal has been measured using monochromatic synchrotron radiation. The self-absorption effect in the spectra is shown to be very small in our experimental geometry. From the quantitative analysis of spectra recorded at different excitation energies, the L3/L2 emission intensity ratio and the partial Auger width are extracted. High-energy satellite features on the L3 emission line are separated by a subtraction procedure. The satellite intensity is found to be slowly increasing for excitation energies between the L3, L2, and L1 core-level thresholds due to shake-up and shake-off transitions. As the excitation energy passes the L2 threshold, a step of rapidly increasing satellite intensity of the L3 emission is found due to additional Coster-Kronig processes.
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| 9. |
- Magnuson, Martin, et al.
(författare)
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Resonant Auger spectroscopy at the L2,3 shake-up thresholds as a probe of electron correlation effects in nickel
- 1998
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 58:7, s. 3677-3681
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Tidskriftsartikel (refereegranskat)abstract
- The excitation energy dependence of the three-hole satellites in the L3-M45M45 and L2-M45M45 Auger spectra of nickel metal has been measured using synchrotron radiation. The satellite behavior in the nonradiative emission spectra at the L3 and L2 thresholds is compared and the influence of the Coster-Kronig channel explored. The three-hole satellite intensity at the L3 Auger emission line reveals a peak structure at 5 eV above the L3 threshold attributed to resonant processes at the 2p53d9 shake-up threshold. This is discussed in connection with the 6-eV feature in the x-ray-absorption spectrum.
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| 10. |
- Magnuson, Martin, 1965-, et al.
(författare)
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Resonant inelastic soft X-ray scattering spectra at the nitrogen and carbon K-edges of poly(pyridine-2,5-diyl)
- 1999
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - 0368-2048 .- 1873-2526. ; 101-103, s. 573-578
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Tidskriftsartikel (refereegranskat)abstract
- Resonant inelastic scattering measurements of the conjugated polymer, poly(pyridine-2,5-diyl) have been performed at the nitrogen and carbon K-edges using synchrotron radiation. For comparison, molecular orbital calculations of the spectra have been carried out with the repeat unit as a model molecule of the polymer chain. The resonant emission spectra show depletion of the π electron bands which is consistent with symmetry selection and momentum conservation rules. The depletion is most obvious in the resonant inelastic scattering spectra of carbon while the nitrogen spectra are dominated by lone pair n orbital emission of σ symmetry and are less excitation energy dependent. By comparing the measurements to calculations an isomeric dependence of the resonant spectra is found giving preference to two of the four possible isomers in the polymer.
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