Electronic structure of biphenyl on Si(100)

M. Cranney, G. Comtet, G. Dujardin, J. W. Kim, T. U. Kampen, K. Horn, M. Mamatkulov, L. Stauffer, and Ph. Sonnet

Phys. Rev. B 76, 075324 – Published 14 August 2007

Abstract

We report the study of both occupied and unoccupied electronic states of biphenyl adsorbed on Si(100) by using synchrotron radiation ultraviolet photoemission spectroscopy, x-ray photoemission spectroscopy, and near-edge x-ray absorption fine structure spectroscopy. The results are compared with calculations of the occupied densities of states. Evidence is given of two main effects: (i) a down shift in energy of the second highest occupied molecular orbital of the strongly chemisorbed configuration at room temperature compared to the weakly chemisorbed configuration at low temperatures and (ii) an energy splitting of some of the occupied and unoccupied states due to the different interactions of the two phenyl rings of the molecule. The electronic structure of biphenyl on Si(100) appears to be an appropriate test for state of the art experimental and theoretical methods.

Received 24 October 2006

DOI:https://doi.org/10.1103/PhysRevB.76.075324

Authors & Affiliations

M. Cranney, G. Comtet, and G. Dujardin

Laboratoire de Photophysique Moléculaire, Université Paris-Sud, Bâtiment 210, 91405 Orsay, France

J. W. Kim, T. U. Kampen, and K. Horn

Fritz-Haber-Institut der Max-Plank-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany

M. Mamatkulov, L. Stauffer, and Ph. Sonnet

Laboratoire de Physique et de Spectroscopie Electronique, CNRS UMR 7014, Université de Haute Alsace, 4 rue des frères Lumière, F-68093 Mulhouse Cedex, France

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Vol. 76, Iss. 7 — 15 August 2007

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Images

Figure 1
Atomic structure of biphenyl on a Si(100) surface in (a) the weakly chemisorbed configuration and (b) the strongly chemisorbed configuration. The gray, black, and white balls correspond to silicon, carbon, and hydrogen atoms, respectively.Reuse & Permissions
Figure 2
Valence band photoemission spectra of the $Si (100) − 2 \times 1$ surface at room temperature and grazing incidence (10°) (a) before and (b) after submonolayer biphenyl exposure. The biphenyl exposure for curve (b) is $6 L$ . (c) is obtained by subtracting (a) from (b). (d) is the valence band photoemission spectrum of condensed biphenyl. For all spectra, the photon energy is $65 eV$ . The arrows indicate the silicon surface state band in (a) and the first and second HOMO bands of adsorbed biphenyl in (c). Binding energies are relative to the Fermi level.Reuse & Permissions
Figure 3
Left part: Details of the valence band photoemission spectra at low temperature $(80 K)$ after subtraction of the corresponding spectra of the clean Si(100) surface. The biphenyl exposure is $2.7 L$ and the photon energy is $65 eV$ : (a) grazing incidence (10°) and (b) magic angle incidence (54°). The spectra have been decomposed into three bands ( $B_{1}$ , $B_{2}$ , and $B_{3}$ ). The extra band in (b) is due to some oxygen pollution. Right part: Calculated occupied densities of states of biphenyl on Si(100). (c) Density of states of the weakly chemisorbed biphenyl projected on the free phenyl ring (dashed-dotted line) and the butterfly phenyl ring (dashed line). (d) Density of states of the weakly chemisorbed biphenyl integrated over the whole molecule. Binding energies are relative to the Fermi level.Reuse & Permissions
Figure 4
Left part: Details of the valence band photoemission spectra at room temperature $(300 K)$ after subtraction of the corresponding spectra of the clean Si(100) surface. The biphenyl exposure is $6 L$ [as for Fig. 2b] and the photon energy is $65 eV$ : (a) grazing incidence (10°) and (b) magic angle incidence (54.7°). Each spectrum has been decomposed into two bands ( $B_{1}$ and $B_{3}$ ). The extra band in (b) is due to some oxygen pollution. Right part: Calculated occupied densities of states of biphenyl on Si(100). (c) Density of states of the strongly chemisorbed biphenyl projected on the butterfly phenyl ring (dashed line) and the dissociated phenyl ring (dashed-dotted line). (d) Density of states of the strongly chemisorbed biphenyl integrated over the whole molecule. Binding energies are relative to the Fermi level.Reuse & Permissions
Figure 5
NEXAFS spectra of biphenyl: (a) condensed on Si(100) and [(b)–(e)] adsorbed on Si(100). (b) Grazing incidence (10°) and low temperature $(80 K)$ . (c) Magic angle (54.7°) incidence and low temperature $(80 K)$ . (d) Grazing incidence (10°) and room temperature. (e) Magic angle incidence (54.7°) and room temperature. The uncertainty on the photon energy is $\pm 0.12 eV$ , while the photon energy resolution is $0.25 eV$ . The NEXAFS spectra have been corrected for the transmission of the beamline by dividing the NEXAFS signal by the signal of a golden mesh set at the input of the experimental chamber.Reuse & Permissions
Figure 6
$C 1 s$ photoemission spectra after biphenyl adsorbed on $Si (100) − 2 \times 1$ at (a) $80 K$ and (b) $300 K$ . The photon energy is $330 eV$ .Reuse & Permissions

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