| 1. |
- Brena, Barbara, et al.
(author)
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Equivalent core-hole time-dependent density functional theory calculations of carbon 1s shake-up states of phthalocyanine
- 2004
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 70:19, s. 195214-
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Journal article (peer-reviewed)abstract
- The shake-up transition energies of the carbon 1s photoelectron spectrum of metal-free phthalocyanine (H2Pc) have been calculated by means of time-dependent density functional theory, for which an equivalent core approximation is adopted. Model calculations for the C 1s shake-up states of benzene are in excellent agreement with the latest experimental results. The complex C 1s shake-up structures associated with the aromatic and pyrrole carbons in the phthalocyanine are computed, as well as their ionization potentials. They allow us to determine the origin of the anomalous intensity ratio between the pyrrole and benzene carbons in a high resolution C 1s photoelectron spectrum measured for a H2Pc film, as due to a benzene-related shake-up contribution, hidden under the pyrrole main intensity feature.
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| 2. |
- Granroth, Sari, et al.
(author)
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Investigation of interface properties of Ni/Cu multilayers by high kinetic energy photoelectron spectroscopy
- 2009
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In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121 .- 1550-235X. ; 80:9
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Journal article (peer-reviewed)abstract
- High kinetic-energy photoelectron spectroscopy (HIKE) or hard x-ray photoelectron spectroscopy has been used to investigate the alloying of Ni/Cu (100) multilayers. Relative intensities of the corelevels and their chemical shifts derived from binding energy changes are shown to give precise information on physicochemical properties and quality of the buried layers. Interface roughening, including kinetic properties such as the rate of alloying, and temperature effects on the processes can be analyzed quantitatively. Using HIKE, we have been able to precisely follow the deterioration of the multilayer structure at the atomic scale and observe the diffusion of the capping layer into the multilayer structure which in turn is found to lead to a segregation in the ternary system. This is of great importance for future research on multilayered systems of this kind. Our experimental data are supplemented by first-principles theoretical calculations of the core-level shifts for a ternary alloy to allow for modeling of the influence of capping materials on the chemical shifts.
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| 3. |
- Karis, O., et al.
(author)
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High-kinetic-energy photoemission spectroscopy of Ni at 1s: 6-eV satellite at 4 eV
- 2008
-
In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121 .- 1550-235X. ; 78:23, s. 3-3
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Journal article (peer-reviewed)abstract
- Electron correlations are responsible for many profound phenomena in solid-state physics. A classical example is the 6-eV satellite in the photoelectron spectrum of Ni. Until now the satellite structure has only been investigated at the L shell and more shallow levels. Here we report a high-kinetic-energy photoemission spectroscopy (HIKE) investigation of Ni metal. We present 1s and 2p photoelectron spectra, obtained using excitation energies up to 12.6 keV. Our investigation demonstrates that the energy position of the satellite relative to the main line is different for the 1s and the 2p levels. In combination with electronic structure calculations, we show that this energy shift is attributed to unique differences in the core-valence coupling for the K and L-2,L-3 shells in 3d transition metals, resulting in different screening of the core holes.
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| 4. |
- Kjeldgaard, Lisbeth, et al.
(author)
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Intramolecular vibronic dynamics in molecular solids: C60
- 2005
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In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 72:20
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Journal article (peer-reviewed)abstract
- Vibronic coupling in solid C60 has been investigated with a combination of resonant photoemission spectroscopy (RPES) and resonant inelastic x-ray scattering (RIXS). Excitation as a function of energy within the lowest unoccupied molecular orbital resonance yielded strong oscillations in intensity and dispersion in RPES, and a strong inelastic component in RIXS. Reconciling these two observations establishes that vibronic coupling in this core hole excitation leads to predominantly inelastic scattering and localization of the excited vibrations on the molecule on a femtosecond time scale. The coupling extends throughout the widths of the frontier valence bands.
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| 5. |
- Käämbre, Tanel, et al.
(author)
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Bulk electronic structure of K3C60 as revealed by soft x-rays
- 2007
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:19, s. 195432-
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Journal article (peer-reviewed)abstract
- We present C 1s x- ray absorption, x- ray emission, and resonant inelastic x- ray scattering (RIXS ) spectra of single- phase crystalline K3C60. The comparison to valence- band photoelectron spectra from the same sample facilitates identification of the contribution from surface and bulk electronic states in the latter. Bulk- sensitive techniques show that the valence bands of K3C60 and pure C-60 are characterized by spectral features of similar width, in agreement with the predictions of band- structure calculations. Symmetry selectivity in the RIXS process allows us to assign peaks in the C 1s absorption spectrum, demonstrating a close correspondence with pure C-60 also in the conduction band. The symmetry selectivity is as pronounced in K3C60 as in pure C-60, indicating that the local C-60 symmetry is not appreciably affected by the K doping, either in the ground state or intermediate state, on the time scale of 6 fs.
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| 6. |
- Magnuson, M., et al.
(author)
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Angular-dependent resonant-photoemission processes at the 2p thresholds in nickel metal
- 1999
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 60:4, s. 2436-2440
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Journal article (peer-reviewed)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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| 7. |
- Magnuson, Martin, et al.
(author)
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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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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 58:7, s. 3677-3681
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Journal article (peer-reviewed)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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| 8. |
- Ng, May Ling, et al.
(author)
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Effect of substrate nanopatterning on the growth and structure of pentacene films
- 2010
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:11, s. 115449-
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Journal article (peer-reviewed)abstract
- The effect of modulating the structure of thin pentacene (C22H14) films by a nanopatterned inert substrate, known as hexagonal boron nitride nanomesh, is reported. Films of different thickness are grown and characterized by x-ray absorption, core-level photoemission, low-energy electron microscopy, microbeam low-energy electron diffraction, and scanning tunneling microscopy. Initially the pentacene molecules adsorb with the molecular plane lying flat on the substrate but they tend to flip up with increasing coverage, forming well-ordered monolayer-thick islands of upright molecules with low nucleation density. The herringbone packing of the upright molecules is observed with scanning tunneling microscopy. The electronic structure of the adsorbed molecules is very similar to that of the gas-phase pentacene, implying weak interaction with the substrate and between the molecules. The periodic corrugation of the substrate surface causes the monolayer of upright pentacene molecules to form two different coincidence superstructures. The lattice parameters of the pentacene unit cell for each of these two substrate-induced domains are determined from the microdiffraction patterns. Both domains can occur in several equivalent configurations, thus resulting in a number of twins with a typical size of a few micrometers. The first monolayer grows in a layer-by-layer mode until it is completed while the second monolayer forms diffusion-limited fractal islands. Upon annealing, the pentacene films are thermally stable up to approximately 80 degrees C and thereafter the onset of desorption is observed.
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| 9. |
- Peredkov, Sergey, et al.
(author)
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Free nanoscale sodium clusters studied by core-level photoelectron spectroscopy
- 2007
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:23, s. 235407-
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Journal article (peer-reviewed)abstract
- Free sodium metal clusters have been studied by probing the Na2p core level using x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The development of electronic structure with size has been studied and discussed in comparison with the atom, dimer, and solid. Information on cluster metallic properties, size, and temperature has been deduced from the XPS measurements. For the large ⟨N⟩>103 Na clusters, the surface and bulk sites have been separated in the photoelectron signal. Auger spectra allowed extracting the information on the valence band. The present study introduces core-level spectroscopies XPS and AES into the field of free neutral metal cluster research.
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| 10. |
- Peredkov, Sergey, et al.
(author)
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Size determination of free metal clusters by core-level photoemission from different initial charge states
- 2007
-
In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121 .- 1550-235X. ; 76:8
-
Journal article (peer-reviewed)abstract
- We present the study of free nanoscale lead clusters using photoelectron spectroscopy and synchrotron radiation. Pb 5d core-level spectra reveal the presence of different initial charge states of the clusters created by the magnetron-based source. We suggest a method for determining the cluster size from the charge-dependent core level binding energies. Both the core-level and the valence spectra demonstrate that we have created free metallic clusters with essentially the same electronic structure as the solid.
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