Plenarvorträge - DPG-Tagungen

Symposium Organic and Hybrid Systems for Future Electronics Donnerstag
or bionic devices require a high degree of functionality as well as a good
stability of surfaces against degradation. In this context, the nanopatterning
of organically modified surfaces has attracted great attention
because such functionalized surfaces offer an excellent passivation and
at the same time the possibility to attach different biological species
(including DNA, proteins and complex systems). In the present work,
strategies for the nanopatterning of chemically modified silicon surfaces
using different lithographic approaches will be presented. It will be shown
that organic monolayers can be used as a new class of organic-based resists
for direct electron-beam writing as well as atomic force microscope
nanoscratching. The use of organic monolayers as positive or negative
resists will be highlighted by exploiting the contrast in reactivity via
chemical deposition (electroless technique) and plating of metals. The
high resolution achieved through the use of such organic-based resists
will be discussed.The processes presented here open new perspectives for
selective deposition and direct patterning of Si surfaces and can be used
not only for chemical and electrochemical nanogrowth but also for the
nanopatterning of chemical and relevant biological species on semiconductor
surfaces.
SYOH 5.10 Do 18:00 B
Blinking and Emission Quenching of CdSe Nanocrystals in Organic
Environments — •Thomas Blaudeck 1 , Abey Issac 2 , Frank
Cichos 1 , Edward Zenkevich 3 , Alexander Shulga 3 , and Christian
von Borczyskowski 2 — 1 Institut für Physik 123705, TU Chemnitz,
09107 Chemnitz — 2 Institut für Physik 121501, 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
The interaction of ZnS capped CdSe nanocrystals with their environment
is studied on an ensemble and single nanocrystal (NC) level. Individual
CdSe NC’s show an emission intermittency (blinking), which
is commonly related to an NC photo-ionization by electron tunneling.
The statistics of this blinking is found to be independent of the studied
NC even though NCs may differ in size and local structure of the
surrounding polymer matrix. We analyze the obtained blinking statistics
in terms of charge diffusion through trap states in the NCs vicinity and
further compare this to current blinking model. Despite the insensitivity
of the blinking process to the surrounding polymer matrix a strong interaction
between CdSe NCs and pyridyl containing porphyrin molecules
is found. The porphyrin molecules self-organize on the NC surface by
ligation effects. The interaction of porphyrin and NC introduces a fast
non-radiative decay of the NC emission, which is ascribed to an electron
transfer process by electron tunneling. The dependence of this tunneling
process on the NC size is discussed.
SYOH 5.11 Do 18:00 B
Temperature-Dependent Growth of Porphyrin and Phthalocyanine
Thin Films on Modified Silicon Surfaces — •Christian
Kelting 1 , Ossamah Abdallah 2 , Marinus Kunst 2 , Natalia
Bazyakina 3 , Dieter Wöhrle 3 , and Derck Schlettwein 1 —
1 Physical Chemistry 1, University of Oldenburg, Germany — 2 Hahn-
Meitner- Institute, Berlin, Germany — 3 Institute of Organic and
Macromolecular Chemistry, University of Bremen, Germany
Films of phthalocyaninatozinc (PcZn) and Tetraphenylporphyrinatozinc
(TPPZn) were evaporated on thin films of microcrystalline Si and
on hydrogen-terminated Si-wafers (111) as a model surface for microcrystalline
Si under conditions of its preparation. The goal is to embed
molecular sensitizers into microcrystalline Si as a new concept for thin
film solar cells. The maximum substrate temperature for a successful deposition
of PcZn and TPPZn was determined to 523 K for PcZn and 423
K for TPPZn on H-Si (111). UV-Vis differential reflection spectroscopy
was measured in situ. At 300 K, a 50 nm PcZn film survived for 5h, but
slowly evaporated during this time. The morphology of the deposited
films was investigated by atomic force microscopy. Larger particles with
well- defined shape indicating crystallinity of the films were detected at
these higher substrate temperatures. Changes in the crystal structure
of PcZn were also observed on the silicon substrates. The alpha- modification
of PcZn was found in depositions at 298 K whereas the betamodification
was formed at 523 K.
SYOH 5.12 Do 18:00 B
The influence of carbon on the mono- and multilayer growth of
p-quaterphenyl on Au(111) — •Adolf Winkler, Stefan Muellegger,
Thomas Haber, and Roland Resel — Solid State Physics,
Graz University of Technology
The tailoring of the growth mode of ultra-thin organic films is of utmost
importance for the application of electronic and optoelectronic devices.
As a model system we have studied the monolayer adsorption and the
multilayer growth of p-quaterphenyl on clean and carbon covered gold
(111) surfaces. TDS, XPS, LEED and XRD-pole figure technique have
been applied for these investigations. In TDS, the monolayer peaks are
quite different for the Au(111) and Au(111)+C surface. Also LEED shows
pronounced differences. The evaluation of the LEED patterns, in combination
with quantitative TDS, suggests a monolayer structure with flat
lying and side tilted 4P molecules on the clean, but with only side tilted
molecules on the C-covered surface. These different monolayer structures
lead to different multilayer film structures, as verified by XRD-pole figure
technique and XPS. In the former case island growth is preferred,
whereas in the latter case layer-like growth dominates.
SYOH 5.13 Do 18:00 B
Morpholoy and growth of organic semiconductor films on metal
surfaces — •S. Söhnchen, S. Lukas, G. Beernink, K. Hänel, A.
Birkner, G. Witte, and C. Wöll — Physikalische Chemie I, Ruhr-
Universitaet Bochum
Organic semiconducting materials have experienced a tremendous
amount of attention because of the recent breakthrough in using such
materials as active components in electronic or optoelectronic devices.
Of particular interest for an optimization of such devices is a detailed
understanding of the crystalline structure and growth properties of thin
organic semiconductor films deposited on inorganic substrates.
In this talk we compare the growth properties observed for pentacene
and perylene films grown by OMBE on copper and gold
single crystal surfaces as well as on a SAM modified gold surface.
Although some of these films are well ordered and partly reveal even
an epitaxial growth relation with respect to the substrate [1] they all
have a large tendency for dewetting which causes the formation of islands.
[1] Lukas et al. Chem. Phys. Chem (in press)
SYOH 5.14 Do 18:00 B
The Growth of Pentacene on Gold — •F.-J. Meyer zu Heringdorf
1,2 , M.C. Reuter 1 , and R.M. Tromp 1 — 1 IBM T.J. Watson
Research Center, Yorktown Heights, USA — 2 present address:Inst. für
Laser- und Plasmaphysik, Universität Duisburg-Essen (Campus Essen)
We used Low Energy Electron Microscopy and Atomic Force Microscopy
to compare the growth of pentacene on Si(111) with the growth
of pentacene on Au. In the LEEM Au films are prepared on Si(111)
at elevated temperatures and their formation is monitored using quasisimultaneous
imaging at different dark field conditions. At low coverages,
Au forms a (5 × 2) reconstruction on the Si(111) substrate, and pentacene
is observed to grow in the thin film phase, similar to growth on
clean silicon. At coverages beyond 3/4 ML of Au, however, a ( √ 3 × √ 3)
reconstruction is formed that causes the orientation of the pentacene
film to rotate by almost 90 ◦ . The same result is found for pentacene on
thick polycrystalline Au films. The adsorption of organic self-assembled
monolayers (SAMs) prior to deposition of pentacene has been reported
to improve the electrical contact between Au and pentacene. Here we
show that thiol based SAMs on Au can restore the growth direction of
pentacene to a crystal orientation as seen on Si. This demonstrates that
carefully chosen organic substrate termination layers are likely to play a
key role in the development of organic thin film semiconductor technology.
SYOH 5.15 Do 18:00 B
Dislocation Arrangements in Pentacene Films — •Bert Nickel
— Ludwig-Maximilians-Universität München
Organic molecules are currently at the focus of many research programms
due to their applications in molecular electronics. Among the
various materials under investigation, pentacene (C22H14), a long, flat,
aromatic molecule is particularly promising, in part because pentacene
easily forms layered crystals if deposited onto flat, inert surfaces, resulting
in highly anisotropic transport properties. We have studied the
growth of pentacene films (2-8 monolayers) on modified Si-wafer surfaces
by means of synchrotron x-ray diffraction. A quantitative analysis of the