Untersuchung der elektronischen Struktur der Li induzierten Si(111)-(3x1)-Rekonstruktion mittels Photoemission und ^8Li-beta-NMR
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Philipps-Universität Marburg
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Abstract
The electronic structure of the Si(111)-(3x1)-Li
surface has been investigated by angular resolved photoemission
spectroscopy (ARPES) and ^8Li beta-detected nuclear magnetic
resonance experiments. The (3x1) reconstruction is well
described by the HCC- (honeycomb-chain-channel) model and
possesses one Li atom per surface unit cell corresponding to a
Li coverage of 1/3 of a monolayer (ML). Single domain
reconstructed (3x1) surfaces were used for the ARPES
experiments. The usage of this surfaces in connection with an
improved energy resolution and an optimized photon energy led
to a significant improvement of previous photoemission data.
Parallel to the quasi one-dimensional Li chains a very
pronounced dispersionless surface state at E-E_{VBM} ~ -0.9 eV
was observed. It is shifted by -0.31 eV compared to the
prediction of LDA (local density approximation) calculations
based on the HCC-model. This shift can probably be related to
disregarded electron correlations in the LDA band structure
calculations. A previous explanation by a combination of two
experimentally unresolved states can be ruled out due to the
improved energy resolution of our experiment. In LEED- (low
energy electron diffraction) experiments a fully (3x1)
reconstructed surface was already observed at a Li coverage of
0.29 ± 0.02 ML. At this coverage and at a surface temperature
of 100 K a nuclear spin relaxation rate compatible with zero
(alpha = 0.007 ± 0.017 s^-1) was measured. At higher
temperatures exponentially rising relaxation rates were
observed. Both facts can be explained by a model based on a two
dimensional donor-level about 100 meV below the conduction
band. This donor level may be induced by the Li additionally
adsorbed during the relaxation experiments. Such a relaxation
mechanism was already observed on the semiconducting
Si(111)-(1x1):H surface. At a Li coverage of 0.47 ML (i.e.
(3x1) reconstruction plus 0.14 ML additional Li) a
"Korringa"-like nuclear spin relaxation was observed pointing
to a metallic surface due to the additional Li coverage. At
higher temperatures an additional relaxation process induced by
diffusion of the Li on the surface seems to be
present.
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Dates
Created: 2003Issued: 2003-12-22Updated: 2011-08-10
Faculty
Fachbereich Physik
Publisher
Philipps-Universität Marburg
Language
ger
Data types
DoctoralThesis
Keywords
Surface states, band structure, electron density of statesClean metal, semiconductor, and insulator surfacesband structure , photoemissionNuclear magnetic resonance and relaxation (see also 33.25.+k Nuclear resonance and relaxation in atomic and molecular physics and 82.56.-b Nuclear magnetic resonance in physical chemistry and chemical physics)Impurity and defect levels; energy states of adsorbed speciesElemental semiconductorsNMRSurface
DFG-subjects
Oberflächenspektroskopie , HalbleiteroberflächeOberflächenzustandSilicium, LithiPhotoelektronenspektroskopie , Beta-NMR-Spektroskopie
DDC-Numbers
530
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Bromberger, Christian (128629177): Untersuchung der elektronischen Struktur der Li induzierten Si(111)-(3x1)-Rekonstruktion mittels Photoemission und ^8Li-beta-NMR. : Philipps-Universität Marburg 2003-12-22. DOI: https://doi.org/10.17192/z2003.0740.
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This item has been published with the following license: In Copyright