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Sodium and potassium monolayers on Be(0001) investigated by photoemission and electronic structure calculations

Algdal, J.; Thiagarajan, Balasubramanian LU ; Breitholtz, M.; Chis, V.; Hellsing, B.; Lindgren, S. -A. and Wallden, L. (2008) In Physical Review B (Condensed Matter and Materials Physics) 78(8).
Abstract
Photoemission spectra show that Be(0001) surface states shift to lower energy with increasing Na or K coverage in the monolayer range. At an intermediate monolayer coverage a quantum well state appears near the Fermi edge and shifts to lower energy reaching saturation energy at full monolayer coverage. At full monolayer coverage low energy electron diffraction shows 2 X 2 order for K while Na forms an incommensurate close-packed structure aligned with the substrate. As a result of the different structures, the photoemission spectra show qualitative differences that are explained by diffraction. First-principles calculations for Be(0001) and p(2 X 2)K/Be(0001) reproduce reasonably the measured energy shifts and dispersions. Spectra recorded... (More)
Photoemission spectra show that Be(0001) surface states shift to lower energy with increasing Na or K coverage in the monolayer range. At an intermediate monolayer coverage a quantum well state appears near the Fermi edge and shifts to lower energy reaching saturation energy at full monolayer coverage. At full monolayer coverage low energy electron diffraction shows 2 X 2 order for K while Na forms an incommensurate close-packed structure aligned with the substrate. As a result of the different structures, the photoemission spectra show qualitative differences that are explained by diffraction. First-principles calculations for Be(0001) and p(2 X 2)K/Be(0001) reproduce reasonably the measured energy shifts and dispersions. Spectra recorded for the shallow alkali-metal core levels show that the adlayer is inhomogeneous in art intermediate coverage range. While this is not noted when the valence state energies are measured a linewidth change observed for one of the surface states is ascribed to this inhomogeneity. It is suggested that the onset of inhomogeneity is associated with the occupation of states in the quantum well band. Occupation of these states, which are highly localized to the adlayer, gives metal character to the layer over an increasing area as the coverage is increased making the film homogeneous at high monolayer coverage. An anomalous emission line is observed for both Na and K as a low energy companion to the quantum well state line becoming increasingly separated from this as the coverage increases. We suggest that the satellite is due to an energy loss associated with collective oscillations in the overlayer. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Physical Review B (Condensed Matter and Materials Physics)
volume
78
issue
8
publisher
American Physical Society
external identifiers
  • wos:000259406900015
  • scopus:49249137315
ISSN
1098-0121
DOI
10.1103/PhysRevB.78.085102
language
English
LU publication?
yes
id
7372d436-8ae7-4734-a18c-4cee51a068f7 (old id 1287217)
date added to LUP
2009-01-28 09:19:23
date last changed
2017-01-01 05:55:30
@article{7372d436-8ae7-4734-a18c-4cee51a068f7,
  abstract     = {Photoemission spectra show that Be(0001) surface states shift to lower energy with increasing Na or K coverage in the monolayer range. At an intermediate monolayer coverage a quantum well state appears near the Fermi edge and shifts to lower energy reaching saturation energy at full monolayer coverage. At full monolayer coverage low energy electron diffraction shows 2 X 2 order for K while Na forms an incommensurate close-packed structure aligned with the substrate. As a result of the different structures, the photoemission spectra show qualitative differences that are explained by diffraction. First-principles calculations for Be(0001) and p(2 X 2)K/Be(0001) reproduce reasonably the measured energy shifts and dispersions. Spectra recorded for the shallow alkali-metal core levels show that the adlayer is inhomogeneous in art intermediate coverage range. While this is not noted when the valence state energies are measured a linewidth change observed for one of the surface states is ascribed to this inhomogeneity. It is suggested that the onset of inhomogeneity is associated with the occupation of states in the quantum well band. Occupation of these states, which are highly localized to the adlayer, gives metal character to the layer over an increasing area as the coverage is increased making the film homogeneous at high monolayer coverage. An anomalous emission line is observed for both Na and K as a low energy companion to the quantum well state line becoming increasingly separated from this as the coverage increases. We suggest that the satellite is due to an energy loss associated with collective oscillations in the overlayer.},
  author       = {Algdal, J. and Thiagarajan, Balasubramanian and Breitholtz, M. and Chis, V. and Hellsing, B. and Lindgren, S. -A. and Wallden, L.},
  issn         = {1098-0121},
  language     = {eng},
  number       = {8},
  publisher    = {American Physical Society},
  series       = {Physical Review B (Condensed Matter and Materials Physics)},
  title        = {Sodium and potassium monolayers on Be(0001) investigated by photoemission and electronic structure calculations},
  url          = {http://dx.doi.org/10.1103/PhysRevB.78.085102},
  volume       = {78},
  year         = {2008},
}