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Plenarvorträge - DPG-Tagungen

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Oberflächenphysik Montag<br />

O 14.54 Mo 18:00 Bereich C<br />

A prove of the spreader-bar approach: Fabrication and characterization<br />

of heterogeneous monomolecular films — •Andrey<br />

Shaporenko 1 , Thomas Hirsch 2 , Vladimir Mirsky 2 , and Michael<br />

Zharnikov 1 — 1 Angewandte Physikalische Chemie, Universität Heidelberg,<br />

69120 Heidelberg — 2 Institut für Analytische Chemie, Chemo- und<br />

Biosensorik, Universität Regensburg, 93040 Regensburg<br />

The aim of the work is a development of a new technology for simple<br />

formation of nanostructures with controlled shape and distribution in<br />

monomolecular films. The technology is based on combination of a selfassembly<br />

of thiol compounds on metals and an approach of molecular<br />

spreader-bars. Through such a combination, mixed monomolecular films<br />

with a defined size of structural elements can be formed and subsequently<br />

used as a platform for biological and chemical research and sensor fabrication.<br />

At an initial stage of the project, several combinations of relevant<br />

molecular constituents have been tested, including simple aliphatic and<br />

aromatic thiols and large conjugated molecules with and without specific<br />

anchor groups. The resulting monomolecular films have been characterized<br />

by several complementary experimental techniques, such as X-ray<br />

photoelectron spectroscopy, near-edge X-ray absorption fine structure<br />

spectroscopy, X-ray absorption spectromicroscopy, and infrared reflection<br />

absorption spectroscopy. Conclusions on the chemical composition,<br />

orientation, and lateral distribution of the molecular constituents were<br />

driven. Based on these conclusions, both the film fabrication procedure<br />

and the selection of the molecular building blocks have been optimized.<br />

O 14.55 Mo 18:00 Bereich C<br />

UV-photoinduced modification and surface anisotropy of<br />

polyimide studied by X-ray absorption spectroscopy and<br />

spectromicroscopy — •Michael Zharnikov 1 , Yukio Ouchi 2 ,<br />

Masaki Hasegawa 3 , and Andreas Scholl 4 — 1 Angewandte<br />

Physikalische Chemie, Universität Heidelberg, 69120 Heidelberg,<br />

Germany — 2 Department of Chemistry, Nagoya University, Nagoya,<br />

464-8602 Japan — 3 IBM Research, Tokyo Research Laboratory, Yamato,<br />

Kanagawa 242-8502, Japan — 4 Advanced Light Source, Lawrence<br />

Berkeley National Lab, Berkeley, CA 94720 USA<br />

An alignment of liquid crystal (LC) molecules in a flat panel display<br />

is mediated by the anisotropic polyimide (PI) substrate. Whereas a conventional<br />

way to fabricate such a substrate is a mechanical rubbing of a<br />

PI, an alternative approach utilizes the irradiation of PI by linearly polarized<br />

UV-light. To get a basic understanding of the phenomenon of UVlight-induced<br />

anisotropy, we have performed NEXAFS spectromicroscopy<br />

measurements at the C, N, and O K-edges on a series of the polyimide<br />

films treated by linearly polarized UV-light through a mask. Fabricated<br />

patterns could be easily distinguished and imaged both for the parallel<br />

and perpendicular orientation of the electric field vectors of the UV- and<br />

synchrotron light. The UV-induced intensity changes of the characteristic<br />

absorption resonances at all probed absorption edges were monitored<br />

and related to the chemical modification of PI. From the analysis of the<br />

NEXAFS microspectra, the extent of the UV-induced anisotropy could<br />

be estimated in good agreement with our previous spectroscopic results.<br />

O 14.56 Mo 18:00 Bereich C<br />

The Interaction of Benzene Derivatives with Amorphous Solid<br />

Water — •O. Höfft 1 , A. Borodin 1 , U. Kahnert 1 , M. O. Abou-<br />

Helal 1 , S. Krischok 2 , and V. Kempter 1 — 1 Institut für Physik<br />

und Physikalische Technologien, TU Clausthal, Leibnizstr. 4, D–38678<br />

Clausthal–Zellerfeld — 2 Institut für Physik und Zentrum für Mikro– und<br />

Nanotechnologien der TU Ilmenau, P.O. Box 100565, D–98684 Ilmenau<br />

Interfaces between films of benzene derivatives (C6H6; C6H5Cl; ortho–<br />

C6H4OHCl; C5H5N) and solid H2O were studied between 90 and 200K<br />

with metastable impact electron spectroscopy (MIES) and ultraviolet<br />

photoelectron spectroscopy (UPS(HeI and II)): (i) adsorption of the benzene<br />

derivatives on solid water in order to simulate their interaction with<br />

ice particles, and (ii) deposition of water on the organic films in order<br />

to simulate the process of water precipitation. The different behaviour<br />

found for the four studied cases is traced back to the different mobilities<br />

of the molecules with respect to that of water. The interaction between<br />

H2O and the benzene dervatives at the interfaces is discussed on the basis<br />

of qualitative profiles for the free energy for the systems.<br />

O 14.57 Mo 18:00 Bereich C<br />

Electron Dynamics in Alkanethiol Self-Assembled Monolayers<br />

on Ultraflat Gold Films — •S. Dantscher, C. Kennerknecht, S.<br />

Schramm, D. Wolpert, and W. Pfeiffer — Physikalisches Institut,<br />

Universität Würzburg, Am Hubland, 97074 Würzburg, Germany<br />

For the self-assembly process of organic molecules like alkanethiols a<br />

very flat surface is necessary. The roughness on the atomic scale has<br />

to be minimized in order to create atomically flat terraces as large as<br />

possible. In this work thin gold films with a thickness from 500 to 700˚A<br />

were evaporated under UHV conditions on freshly cleaved, heated (650K)<br />

mica sheets. After the evaporation process the surface only showed weak<br />

LEED spots which could be improved by sputtering and heating cycles.<br />

The enlargement of the terrace width up to 200nm was also confirmed<br />

by STM topographies. Adsorption of the alkanethiols took place in an<br />

inert gas atmosphere in order to prevent contamination of the gold surface.<br />

The technique of Time Resolved Two Photon Photo Emission was<br />

used to investigate the influence of the adsorbed SAM layer on electronic<br />

properties of the gold surface like work function and lifetime of excited<br />

states.<br />

O 14.58 Mo 18:00 Bereich C<br />

Normal Incidence X-ray Standing Waves (NIXSW) study of<br />

PTCDA on Ag(111) — •A. Hauschild 1 , M. Sokolowski 1 , and F.<br />

S. Tautz 2 — 1 Institut für Physikalische und Theoretische Chemie , Universität<br />

Bonn, Wegelerstr. 12, 53115 Bonn, Germany — 2 School of Engineering<br />

and Science, International University Bremen, PO Box 750561,<br />

28725 Bremen, Germany<br />

Whereas the adsorption geometries of small molecules on surfaces are<br />

already rather well understood up to now, only little information has<br />

been gained for larger aromatic molecules so far, partly because of experimental<br />

reasons.<br />

PTCDA (3,4,9,10-perylene-tetracarboxylicacid-dianhydrid)<br />

chemisorbs on Ag(111) substrate, forming a commensurate monolayer<br />

with flat lying molecules arranged in a so-called ”herringbone-pattern”.<br />

We have investigated the atomic bonding distances of PTCDA relative<br />

to the Ag(111) by NIXSW measurements performed on the O1s and<br />

C1s level. Since oxygen and carbon are light atoms, the analysis requires<br />

taking into account non-dipolar contributions to the photoemission<br />

yield. First results indicate an averaged bonding distance for the oxygen<br />

atoms of 2.84 ˚A and for the carbon atoms of 2.90 ˚A.<br />

This work was performed in cooperation with C. Stadler, C. Kumpf<br />

and E. Umbach (Universität Würzburg) and supported by the ESRF<br />

(Grenoble, France).<br />

O 14.59 Mo 18:00 Bereich C<br />

Reflexions-Anisotropie-Spektroskopie zur Untersuchung von<br />

adsorbatmodifizierten vizinalen Si(001) Oberflächen — •R.<br />

Passmann 1,2 , M. Wahl 1,2 , M. Gensch 1 , K. Hinrichs 1 , W. Richter<br />

2 und N. Esser 1 — 1 Institut für Spektrochemie und Angewandte<br />

Spektroskopie - Institutsteil Berlin, Albert-Einstein-Str. 9, D-12489<br />

Berlin-Adlershof — 2 TU Berlin, Institut für Festkörperphysik, PN6-1,<br />

Hardenbergstr. 36, D-10623 Berlin<br />

Bestimmte organische Moleküle bilden geordnete Monolagen auf<br />

Si(001) Substraten. Durch geeignet gewählte vizinale Substrate kann<br />

zudem eine Vorzugsrichtung dieser Moleküle entlang bestimmter<br />

Richtungen in der Substratebene erreicht werden. Die damit einhergehende<br />

Modifizierung der anisotropen optischen Eigenschaften kann mit<br />

Reflexions-Anisotropie-Spektroskopie (RAS) untersucht werden.<br />

Optisch anisotrope Cyclopenten/Si(001) sowie Ethylen/Si(001) Grenzflächen<br />

wurden auf vizinalen Si(001) Substraten (4 ◦ offcut in 〈111〉<br />

Richtung) im Ultrahochvakuum präpariert und mit RAS und verschiedenen<br />

komplementären Methoden (LEED, Auger) charakterisiert.<br />

Durch Vergleich der optischen Spektren mit entsprechenden ab-initio<br />

Rechnungen [1] werden Bindungsmodelle für die adsorbatmodifizierten<br />

Si(001) Grenzflächen diskutiert.<br />

[1] W. C. Lu, W. G. Schmidt, J. Bernholc, Phys. Rev. B 68 (11), 115327<br />

(2003)

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