| 1. |
- A. Nojima,, et al.
(författare)
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Calculational aspects of electron-phonon coupling at surfaces
- 2008
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Ingår i: J. Phys: Condens. Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 20
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Tidskriftsartikel (refereegranskat)abstract
- We study the validity of two frequently used approximations in calculations of electron–phonon coupling at surfaces. The rigid-ion approximation is a standard approximation used for the bulk metals. On the basis of density functional theory calculations, we find that for Be this approximation is as valid for surface atoms as for bulk atoms. In addition, the slab method for calculations of a phonon induced surface state lifetime is examined. The convergence of the electron–phonon matrix element with respect to the thickness of the slab is studied for several systems. When the number of slab layers is increased, the net effect of decreasing overlap and increasing number of final states depends strongly on the decay length of the surface state wavefunction and the band structure.
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| 2. |
- A. Nojima,, et al.
(författare)
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Model Eliashberg function for surface states
- 2008
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Ingår i: Applied Surface Science. ; 254:23
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Tidskriftsartikel (refereegranskat)abstract
- We present a simplified procedure for the analysis of the phonon-induced lifetimes of surface states. The model includes information about the electron and phonon structure and is thus more reliable than procedures based on phonon Debye models. We apply the model to calculate the lifetime broadening of Cu(1 1 1) and Al(0 0 1) surface states. The obtained Eliashberg functions and lifetimes are in reasonable agreement with previous detailed studies.
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| 3. |
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| 4. |
- Benedek, Giorgio, et al.
(författare)
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Theory of surface phonons at metal surfaces: recent advances
- 2010
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Ingår i: Journal of Physics: Condensed Matter. - 0953-8984. ; 22:8
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies of the surface dynamics of Al(001) and Cu(111) based on density functional perturbation theory have substantiated the existence of subsurface optical phonon resonances of all three polarizations, thus confirming early predictions of the embedded-atom method. The hybridization of the shear-vertical optical resonance with the longitudinal acoustic phonon branch accounts for the ubiquitous anomalous acoustic resonance as an intrinsic feature of metal surfaces. The DFPT calculation of the phonon-induced surface charge density oscillations shows that helium atom scattering spectroscopy (HAS) can indeed probe subsurface resonances. This opens new perspectives to HAS for the measurement of subsurface phonon dispersion curves in thin films, as proved by recent HAS studies on Pb and Fe ultrathin films on copper. After discussing these recent advances, this paper briefly reviews other important trends of surface dynamics expressed in recent years.
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| 5. |
- Breitholtz, Marcus, 1974, et al.
(författare)
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Overlayer resonance and quantum well state of Cs/Cu(111) studied with angle-resolved photoemission, LEED, and first-principles calculations
- 2007
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Ingår i: Physical Review B. - 1098-0121. ; 75:15, s. 9-
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Tidskriftsartikel (refereegranskat)abstract
- Angle-resolved photoemission spectroscopy and low-energy electron diffraction are used to study submonolayer coverages of Cs on Cu(111) at room temperature (RT) and 170 K. At RT, the Cs saturation coverage is approximately 90% of the full monolayer coverage. The full monolayer is characterized by a quantum well state (QWS) band having an energy of 25 meV below the Fermi level (E-F) in the (Gamma) over bar point and a resonance band extending to energies below the Cu band gap. This is supported by our first-principles calculations. Low-energy electron diffraction shows that the Cs overalyer forms a (2x2) structure over a wide coverage range, in which the QWS has energies from 50 meV above to 25 meV below E-F. The continued energy shift of the QWS after saturation of the diffraction angles is interpreted in terms of vacancies in the overlayer.
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| 6. |
- Carlsson, Anna K, 1966, et al.
(författare)
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High-resolution photoemission from a tunable quantum well: Cu(111)/Na
- 1997
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 56:3, s. 1593 - 1600
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Tidskriftsartikel (refereegranskat)abstract
- High-resolution photoemission (ΔE=5 meV) at a low photon energy (3.82 eV) is used to probe discrete quantum-well-type subband states near, below, and above EF for Cu(111) covered with 2 ML or less of Na. A subband characteristic of the monolayer range shifts gradually to lower energy as the coverage is increased, extending below the Fermi level for coverages above 0.85 ML. Combined with previous observations of shifts for filled and empty states the present results show that the Na monolayer has continuously tunable quantum-well state energies. Beyond the monolayer range quantum-well states characteristic of both one and two atomic layers are observed, indicating growth of the second layer via monolayer high islands. A small downshift, by 25 meV, with increasing coverage in the second layer is ascribed to an increase of the island size. Lorentzian photoemission line shapes are observed for well-ordered samples. The linewidth varies linearly with temprature in the probed range (130–295 K) and this is ascribed to the phonon contribution to the width. Structural disorder leads to an asymmetric line, which is Lorentzian on the steeper, low-kinetic-energy side.
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| 8. |
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| 9. |
- Chis, Vasile, 1977, et al.
(författare)
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Plasmaron excitations in p(2X2)-K/graphite
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121. ; 89:20
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Tidskriftsartikel (refereegranskat)abstract
- Plasmarons formed by the compound of photoelectrons and acoustic surface-plasmon excitations is investigated in the system p(2 × 2)-K/graphite. The physics behind this type of plasmarons (e plasmarons) differs from the physics of plasmarons recently found in graphene, where the loss feature is argued to result from the photohole-plasmon interaction (h plasmarons). Based on first principles methods we calculate the dispersion of the e-plasmaron excitation rate, which yields a broad feature below the parabolic quantum-well band with a peak about 0.4 eV below the quantum-well band.
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| 10. |
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