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@PHDTHESIS{vanStraaten:826345,
author = {van Straaten, Gerben},
othercontributors = {Kumpf, Christian and Sokolowski, Moritz and Klemradt, Uwe},
title = {{G}eometric and electronic properties of heteromolecular
organic monolayers on noble metal substrates studied by
photoemission spectroscopy and {X}-ray standing waves},
volume = {235},
school = {RWTH Aachen University},
type = {Dissertation},
address = {Jülich},
publisher = {Forschungszentrum Jülich GmbH, Zentralbibliothek, Verlag},
reportid = {RWTH-2021-08909},
series = {Schriften des Forschungszentrums Jülich. Reihe
Schlüsseltechnologien = Key technologies},
pages = {1 Online-Ressource (vii, 115 Seiten) : Illustrationen,
Diagramme},
year = {2021},
note = {Druckausgabe: 2021. - Onlineausgabe: 2021. - Auch
veröffentlicht auf dem Publikationsserver der RWTH Aachen
University; Dissertation, RWTH Aachen University, 2020},
abstract = {The primary focus of this study was to analyze
molecule-substrate and molecule-molecule interactions in
heteromolecular monolayers on metallic substrates using a
number of high precision experimental techniques capable of
measuring the electronic and geometric properties of
surfaces and ultrathin films. Therefore the first part of
this works compares the geometric and electronic properties
of two prototypical heteromolecular monolayer systems:
CuPc+PTCDA/Ag(111) and SnPc+PTCDA/Ag(111). For one of these
experimental techniques, the XSW technique, several issues
were recognized that were caused by effects so far not
recognized in the literature. As such, the second part of
this thesis describes improved ways of analyzing NIXSW data,
considering non-dipolar effects and the attenuation of the
measured signal by inelastic scattering. To elaborate, in
the first section, we present a systematic study of the
geometric and electronic properties of hetero-organic
monolayers consisting of SnPc and PTCDA adsorbed on the
Ag(111) surface and we compare these properties with those
of monolayers containing CuPc and PTCDA. The geometric
structures of these layers has been studied with LEED, STM
and the NIXSW technique, while their electronic structure
has been analyzed using ARPES data that has been analyzed
using the photoemission tomography technique.By comparing
the two different systems, we gain insight into the
influence of the phthalocyanine central metal atom on
substrate-mediated interactions in phthalocyanine-PTCDA
heteromolecular monolayers. It is observed that, in
particular, the PTCDA anhydride groups are very sensitive to
the central metal atom of the neighboring phthalocyanines.
In addition to that, considerable differences in the
phthalocyanine molecules are observed as well. First of all,
in both systems charge transfer takes place from the
phthalocyanine fLUMO to the PTCDA fLUMO. While this transfer
is complete in the case of CuPc, leading to a complete
depopulation of the fLUMO, the fLUMO of SnPc is pinned to
the Fermi edge instead, causing it to be partially filled.
Furthermore we observe that the adsorption height of SnPc is
strongly altered after mixing with PTCDA, whereas no change
in adsorption height can be observed for CuPc. We show that
all these differences can be traced back to differences in
the interaction between the phthalocyanine central metal
atom and the substrate. Based on experience obtained during
these measurements, it was realized that several assumptions
underpinning the NIXSW method are not valid under realistic
experimental conditions and in the second section of this
work we reevaluate the theory of the NIXSW method. In
particular, the correction factors that are used to account
for non-dipolar effects in photoelectron-monitored NIXSW
measurements are affected by small yet necessary deviations
from perfect normal incidence. We have shown that neglecting
these effects can lead to significant deviations and
therefor new equations for the calculation of these
correction factors are derived and the magnitude of the
deviation caused by neglecting to account for the
experimental geometry is analyzed for a variety of systems.
Finally, a second effect that is neglected in
photoelectron-monitored NIXSW measurements is the limited
mean-free path of the emitted photoelectrons. We show that
under grazing emission conditions, the obtained parameters
can deviate significantly from the true structural
parameters and that these deviations are angle-dependent. As
a result of this, angle-resolved NIXSW measurements taken
close to grazing conditions contain additional information
about the shape of the atomic distribution function at the
substrate. Two methods for analyzing angle-resolved NIXSW
data are presented, one best suited for recovering the layer
spacing in multilayer systems, and one method suited for
obtaining information about the shape of the distribution
function of poorly ordered adsorbate layers. },
cin = {134110 / 130000},
ddc = {530},
cid = {$I:(DE-82)134110_20140620$ / $I:(DE-82)130000_20140620$},
typ = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
doi = {10.18154/RWTH-2021-08909},
url = {https://publications.rwth-aachen.de/record/826345},
}
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