Plenarvorträge - DPG-Tagungen

Oberflächenphysik Montag
O 14.54 Mo 18:00 Bereich C
A prove of the spreader-bar approach: Fabrication and characterization
of heterogeneous monomolecular films — •Andrey
Shaporenko 1 , Thomas Hirsch 2 , Vladimir Mirsky 2 , and Michael
Zharnikov 1 — 1 Angewandte Physikalische Chemie, Universität Heidelberg,
69120 Heidelberg — 2 Institut für Analytische Chemie, Chemo- und
Biosensorik, Universität Regensburg, 93040 Regensburg
The aim of the work is a development of a new technology for simple
formation of nanostructures with controlled shape and distribution in
monomolecular films. The technology is based on combination of a selfassembly
of thiol compounds on metals and an approach of molecular
spreader-bars. Through such a combination, mixed monomolecular films
with a defined size of structural elements can be formed and subsequently
used as a platform for biological and chemical research and sensor fabrication.
At an initial stage of the project, several combinations of relevant
molecular constituents have been tested, including simple aliphatic and
aromatic thiols and large conjugated molecules with and without specific
anchor groups. The resulting monomolecular films have been characterized
by several complementary experimental techniques, such as X-ray
photoelectron spectroscopy, near-edge X-ray absorption fine structure
spectroscopy, X-ray absorption spectromicroscopy, and infrared reflection
absorption spectroscopy. Conclusions on the chemical composition,
orientation, and lateral distribution of the molecular constituents were
driven. Based on these conclusions, both the film fabrication procedure
and the selection of the molecular building blocks have been optimized.
O 14.55 Mo 18:00 Bereich C
UV-photoinduced modification and surface anisotropy of
polyimide studied by X-ray absorption spectroscopy and
spectromicroscopy — •Michael Zharnikov 1 , Yukio Ouchi 2 ,
Masaki Hasegawa 3 , and Andreas Scholl 4 — 1 Angewandte
Physikalische Chemie, Universität Heidelberg, 69120 Heidelberg,
Germany — 2 Department of Chemistry, Nagoya University, Nagoya,
464-8602 Japan — 3 IBM Research, Tokyo Research Laboratory, Yamato,
Kanagawa 242-8502, Japan — 4 Advanced Light Source, Lawrence
Berkeley National Lab, Berkeley, CA 94720 USA
An alignment of liquid crystal (LC) molecules in a flat panel display
is mediated by the anisotropic polyimide (PI) substrate. Whereas a conventional
way to fabricate such a substrate is a mechanical rubbing of a
PI, an alternative approach utilizes the irradiation of PI by linearly polarized
UV-light. To get a basic understanding of the phenomenon of UVlight-induced
anisotropy, we have performed NEXAFS spectromicroscopy
measurements at the C, N, and O K-edges on a series of the polyimide
films treated by linearly polarized UV-light through a mask. Fabricated
patterns could be easily distinguished and imaged both for the parallel
and perpendicular orientation of the electric field vectors of the UV- and
synchrotron light. The UV-induced intensity changes of the characteristic
absorption resonances at all probed absorption edges were monitored
and related to the chemical modification of PI. From the analysis of the
NEXAFS microspectra, the extent of the UV-induced anisotropy could
be estimated in good agreement with our previous spectroscopic results.
O 14.56 Mo 18:00 Bereich C
The Interaction of Benzene Derivatives with Amorphous Solid
Water — •O. Höfft 1 , A. Borodin 1 , U. Kahnert 1 , M. O. Abou-
Helal 1 , S. Krischok 2 , and V. Kempter 1 — 1 Institut für Physik
und Physikalische Technologien, TU Clausthal, Leibnizstr. 4, D–38678
Clausthal–Zellerfeld — 2 Institut für Physik und Zentrum für Mikro– und
Nanotechnologien der TU Ilmenau, P.O. Box 100565, D–98684 Ilmenau
Interfaces between films of benzene derivatives (C6H6; C6H5Cl; ortho–
C6H4OHCl; C5H5N) and solid H2O were studied between 90 and 200K
with metastable impact electron spectroscopy (MIES) and ultraviolet
photoelectron spectroscopy (UPS(HeI and II)): (i) adsorption of the benzene
derivatives on solid water in order to simulate their interaction with
ice particles, and (ii) deposition of water on the organic films in order
to simulate the process of water precipitation. The different behaviour
found for the four studied cases is traced back to the different mobilities
of the molecules with respect to that of water. The interaction between
H2O and the benzene dervatives at the interfaces is discussed on the basis
of qualitative profiles for the free energy for the systems.
O 14.57 Mo 18:00 Bereich C
Electron Dynamics in Alkanethiol Self-Assembled Monolayers
on Ultraflat Gold Films — •S. Dantscher, C. Kennerknecht, S.
Schramm, D. Wolpert, and W. Pfeiffer — Physikalisches Institut,
Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
For the self-assembly process of organic molecules like alkanethiols a
very flat surface is necessary. The roughness on the atomic scale has
to be minimized in order to create atomically flat terraces as large as
possible. In this work thin gold films with a thickness from 500 to 700˚A
were evaporated under UHV conditions on freshly cleaved, heated (650K)
mica sheets. After the evaporation process the surface only showed weak
LEED spots which could be improved by sputtering and heating cycles.
The enlargement of the terrace width up to 200nm was also confirmed
by STM topographies. Adsorption of the alkanethiols took place in an
inert gas atmosphere in order to prevent contamination of the gold surface.
The technique of Time Resolved Two Photon Photo Emission was
used to investigate the influence of the adsorbed SAM layer on electronic
properties of the gold surface like work function and lifetime of excited
states.
O 14.58 Mo 18:00 Bereich C
Normal Incidence X-ray Standing Waves (NIXSW) study of
PTCDA on Ag(111) — •A. Hauschild 1 , M. Sokolowski 1 , and F.
S. Tautz 2 — 1 Institut für Physikalische und Theoretische Chemie , Universität
Bonn, Wegelerstr. 12, 53115 Bonn, Germany — 2 School of Engineering
and Science, International University Bremen, PO Box 750561,
28725 Bremen, Germany
Whereas the adsorption geometries of small molecules on surfaces are
already rather well understood up to now, only little information has
been gained for larger aromatic molecules so far, partly because of experimental
reasons.
PTCDA (3,4,9,10-perylene-tetracarboxylicacid-dianhydrid)
chemisorbs on Ag(111) substrate, forming a commensurate monolayer
with flat lying molecules arranged in a so-called ”herringbone-pattern”.
We have investigated the atomic bonding distances of PTCDA relative
to the Ag(111) by NIXSW measurements performed on the O1s and
C1s level. Since oxygen and carbon are light atoms, the analysis requires
taking into account non-dipolar contributions to the photoemission
yield. First results indicate an averaged bonding distance for the oxygen
atoms of 2.84 ˚A and for the carbon atoms of 2.90 ˚A.
This work was performed in cooperation with C. Stadler, C. Kumpf
and E. Umbach (Universität Würzburg) and supported by the ESRF
(Grenoble, France).
O 14.59 Mo 18:00 Bereich C
Reflexions-Anisotropie-Spektroskopie zur Untersuchung von
adsorbatmodifizierten vizinalen Si(001) Oberflächen — •R.
Passmann 1,2 , M. Wahl 1,2 , M. Gensch 1 , K. Hinrichs 1 , W. Richter
2 und N. Esser 1 — 1 Institut für Spektrochemie und Angewandte
Spektroskopie - Institutsteil Berlin, Albert-Einstein-Str. 9, D-12489
Berlin-Adlershof — 2 TU Berlin, Institut für Festkörperphysik, PN6-1,
Hardenbergstr. 36, D-10623 Berlin
Bestimmte organische Moleküle bilden geordnete Monolagen auf
Si(001) Substraten. Durch geeignet gewählte vizinale Substrate kann
zudem eine Vorzugsrichtung dieser Moleküle entlang bestimmter
Richtungen in der Substratebene erreicht werden. Die damit einhergehende
Modifizierung der anisotropen optischen Eigenschaften kann mit
Reflexions-Anisotropie-Spektroskopie (RAS) untersucht werden.
Optisch anisotrope Cyclopenten/Si(001) sowie Ethylen/Si(001) Grenzflächen
wurden auf vizinalen Si(001) Substraten (4 ◦ offcut in 〈111〉
Richtung) im Ultrahochvakuum präpariert und mit RAS und verschiedenen
komplementären Methoden (LEED, Auger) charakterisiert.
Durch Vergleich der optischen Spektren mit entsprechenden ab-initio
Rechnungen [1] werden Bindungsmodelle für die adsorbatmodifizierten
Si(001) Grenzflächen diskutiert.
[1] W. C. Lu, W. G. Schmidt, J. Bernholc, Phys. Rev. B 68 (11), 115327
(2003)