Plenarvorträge - DPG-Tagungen

Symposium Organic and Hybrid Systems for Future Electronics Donnerstag
The preliminary results of SEM and confocal fluorescence microscopy
show that the nanoparticle are trapped in the nanowires during the process
of interfacial assembly.
SYOH 5.3 Do 18:00 B
STM Investigation of the Adsorption of C60 Molecules on Vicinal
Si(111)-7x7 Surfaces — •Yu Suzuki, Falk Müller, Thorsten
Kampen, Michael Hietschold, and Dietrich Zahn — Institute of
physics, University of Technology Chemnitz, 09126 Chemnitz, Germany
Vicinal silicon surfaces have attracted much attention as promising
candidates for templates of self-assembled organic nano-structures. The
step edges on vicinal surfaces might serve as preferential adsorption sites
for the molecules, which may result in the self-assembly of molecular
nano-wires.
In this study the adsorption of high symmetrical C60 on vicinal Si(111)-
7x7 surfaces was investigated using scanning tunnelling microscopy under
UHV conditions. The vicinal silicon substrates were first chemically
cleaned by hydrogen peroxide and followed by direct current heating in
UHV. STM showed stepped surface on vicinal silicon after this preparation
procedure. A 7x7 reconstruction was confirmed by LEED and STM.
However, the morphology of the vicinal surfaces were strongly affected
by details of the preparation procedure. The C60 molecule at the edges
showed more stability and less mobility against the manipulation by STM
tip, compared to the ones on terraces of silicon steps.
SYOH 5.4 Do 18:00 B
Self-assembly of highly rigid redox-active nanostructures monitored
by optical second harmonic generation — •Tobias Weidner
1 , Jens Vor der Brüggen 2 , Andreas Krämer 2 , Ulrich
Siemeling 2 , and Frank Träger 1 — 1 Institut für Physik and Center
for Interdisciplinary Nanostructure Science and Technology - CINSaT,
Universität Kassel, Heinrich-Plett-Str. 40, D-34132 Kassel — 2 Institut für
Chemie and Center for Interdisciplinary Nanostructure Science and Technology
- CINSaT, Universität Kassel, Heinrich-Plett-Str. 40, D-34132
Kassel
We have used self-assembly techniques for the preparation of highly
ordered electronically active monolayers on gold substrates. Many compounds
used for self assembly at present are intrinsically flexible due to
flexible spacer units thus limiting the overall film ordering. To resolve this
problem we have synthesized compounds bearing highly rigid π-spacers
and 2, 2 ′ : 6 ′ , 2 ′′ -terpyridin-4 ′ -yl or tripodal tris[(methylthio)methyl]silyl
headgroups, adding to the rigidity of the obtained films. These molecules
have been functionalised with phenyl and ferrocenyl groups. Ferrocene is
a redox-active organometallic unit which is widely used for sensoric and
electronic applications. Adsorption from solution was studied in situ by
optical second harmonic generation (SHG) with submonolayer resolution.
SHG was also used to examine film ordering in real time. The results have
been compared to ellipsometric measurements. The data show that adsorption
leads to the formation of monomolecular films at the interface.
We found that film growth is followed by self-assembly of highly ordered
redox-active ferrocenyl nanostructures.
SYOH 5.5 Do 18:00 B
Luminescence quenching of tetracene molecules adsorbed
on the sapphir surface — •Andreas Langner and Moritz
Sokolowski — Institut für Physikalische und Theoretische Chemie,
Universität Bonn, Wegelerstr. 12, D-53115 Bonn
A surface usually affects the photolumenescence (PL) of adsorbed
molecules. Our aim is to understand the mechanisms which modify the
PL, in order to apply PL spectroscopy to learn something about the
dynamic processes of molecules on surfaces (e.g., mobility, diffusion, rotation
of molecules). So far PL investigations of isolated molecules on well
defined surfaces are missing, partly because on metallic surfaces ultrafast
quenching occurs and no fluorescence is observable.
However, on surfaces of wide gap insulator materials we expect to
obtain PL signal from adsorbed molecules. In particular, we have investigated
tetracene evaporated at 100K on Al2O3(0001). The substrate
was prepared in UHV by Ar + sputtering and annealing in O2 at 1200K.
We control the number of adsorbed molecules very accurately by thermal
desorption. Contrary to our expectation, no fluorescence is observed
for a 0.2 monolayer thick film of presumably isolated molecules. After
annealing to 240K we can measure an increase of the PL signal of the
order of three magnitudes, which is probably due to the growth of 3Dtetracene-crystallites.
We report the evolution of the PL in dependence
of the film thickness and the annealing temperature.
SYOH 5.6 Do 18:00 B
Langmuir-Blodgett monolayer behavior of dinuclear ruthenium(II)trisbipyridine
complexes — •Xiaodong Chen 1 , Frank
Vergeer 2 , Steve Welter 2 , Luisa de Cola 2 , Lifeng Chi 1 , and
Harald Fuchs 1 — 1 Physikalisches Institut, Wilhelm-Klemm-Str. 10,
48149, Muenster, Germany — 2 Molecular Photonics Group, Institute of
Molecular Chemistry, University of Amsterdam, 1018 WV Amsterdam,
The Netherlands
Dinuclear ruthenium complexes have been generating interest as a
class of electroluminescent materials [1]. Langmuir-Blodgett (LB) technique
is a powerful tool for assembling different molecules to build ultrathin
organic films with well-controlled structure and thickness. In the
present report, we used the LB technique to prepare dinuclear ruthe-
nium(II)trisbipyridine complexes monolayers. The complexes contain two
Ru(bpy) 2+
3 moieties and four phenylene units as spacers between the two
ruthenium centers. From the surface pressure-molecular area isotherms
and morphologies, it was found that the complexes possessing long alkyl
chains on one of the Ru(bpy) 2+
3 centers and those without long alkyl
chains show different behaviors. It seems that the introduction of the
alkyl chains in the complexes is indeed necessary to obtain a more homogeneous
film. In addition, the effect of pressure on the morphologies
of monolayers was considered. The results provide basic clues for future
monomolecular layers electroluminescent device preparation.
[1] S. Welter et al. Nature 421, 54 (2003)
SYOH 5.7 Do 18:00 B
Synthese von molekularskaligen Drähten auf DNA-Basis —
•Patrick Nickels, Wendy Huynh und Friedrich Simmel —
Sektion Physik und Center for Nanoscience, Universität München,
Geschwister-Scholl-Platz 1, 80539 München
Die herausragenden molekularen Erkennungseigenschaften von DNA-
Molekülen können für den Aufbau komplexer supramolekularer Netzwerke
genutzt werden. Solche Netzwerke könnten die Grundlage selbstorganisierter
Schaltkreise bilden. Die unzureichenden elektronischen Eigenschaften
von DNA-Molekülen verhindern allerdings ihren unmittelbaren
Einsatz als molekularskalige Komponenten. Ein wesentlicher Schritt
ist daher die Funktionalisierung von DNA-Strängen mit halbleitenden
oder metallischen Materialien. Hier präsentieren wir verschiedene Methoden
zur DNA-gesteuerten Synthese von Metallen, leitfähigen Polymeren
und anorganischen Halbleitern sowie deren rasterkraftmikroskopische
und elektronische Charakterisierung.
SYOH 5.8 Do 18:00 B
Self-Organized Nanocomposites of CdSe Nanocrystals and Porphyrins
— •Abey Issac 1 , Thomas Blaudeck 2 , Frank Cichos 2 ,
Edward Zenkevich 3 , Alexander Shulga 3 , and Christian von
Borczyskowski 1 — 1 Institut für Physik 122501, TU Chemnitz, 09107
Chemnitz — 2 Institut für Physik 123705, TU Chemnitz, 09107 Chemnitz
— 3 Institute of Molecular and Atomic Physics and B.I. Stepanov Institute
of Physics National Academy of Sciences, 70 F. Skaryna Avenue,
220072 Minsk, Belarus
Composites of semiconductor nanocrystals (NC) and organic compounds
open a road to new functional units for optoelectronic applications.
Such composites may be prepared by self-organization of functionalized
organic chromophores on semiconductor NCs. We present results
of spectroscopic studies, where we investigate composites of pyridyl containing
porphyrin molecules and CdSe NCs in solution. The experiments
show a strong quenching of the emission of CdSe NCs even at ratios of the
porphyrin to NC concentration much smaller than one. This is ascribed
to the self-organization of porphyrin molecules on the NC surface by ligation
interactions. The close proximity of NC and porphyrin and their
electronic interaction opens nonradiative channels, which we tentatively
ascribe to an electron transfer process from the NC to the porphyrin.
With increasing number of porphyrin molecules per NC the NC emission
is quenched almost completely. This points to an electron transfer, that
occurs on a much shorter timescale than the emission decay of the NC
which is confirmed by time resolved measurements. The dependence of
the observed emission quenching on the NC size will be discussed.
SYOH 5.9 Do 18:00 B
Nanopatterning of Organically Modified Semiconductor Surfaces
— •Thierry Djenizian, Eugen Balaur, Yan Zhang, and
Patrik Schmuki — Chair for Surface Science and Corrosion, WW4,
University of Erlangen-Nuremberg, Martensstrasse 7, 91058, Erlangen
The preparation, development and integration of practical electronic