Plenarvorträge - DPG-Tagungen

Oberflächenphysik Montag
O 4 Organische Dünnschichten I
Zeit: Montag 11:15–13:15 Raum: H43
O 4.1 Mo 11:15 H43
Optische in situ Spektroskopie der TiOPc-PTCDA-Grenzfläche
— •Thomas Dienel, Holger Proehl, Robert Nitsche, Karsten
Walzer, Torsten Fritz und Karl Leo — Institut für Angewandte
Photophysik, Technische Universität Dresden, 01062 Dresden, Germany
Die Grenzflächen zwischen verschiedenen organischen Molekülen spielen
eine entscheidende Rolle im Aufbau von Bauelementen wie Leuchtdioden
(OLEDs) oder organischen Solarzellen. Um eine definierte Struktur
zu erhalten, wurde mit organischer Molekularstrahlepitaxie Titanylphthalocyanin
(TiOPc) auf einer ebenfalls hochgeordneten 3,4,9,10-Perylen-
Tetracarbonsäure-Dianhydrid-Schicht (PTCDA) abgeschieden.
Die verwendete Differentielle Reflexionsspektroskopie (DRS) gibt uns
die Möglichkeit, die optischen Eigenschaften und ihre Änderung während
des Schichtwachstums zu untersuchen. Für dünne Schichten auf transparenten
Substraten spiegelt das DRS-Signal die Absorption der adsorbierten
Moleküle wieder, und ermöglicht so die Beobachtung des Übergangs
vom Monomerspektrum des Einzelmoleküls zur Kristallabsorption.
Ebenfalls mit einer Auflösung im Submonolagenbereich lässt sich die
Photolumineszenz untersuchen. Dazu wurde die Kristallemission einer
5nm PTCDA-Schicht angeregt und deren Intensität während des Aufwachsens
der TiOPc-Moleküle beobachtet. Mit dem Verschwinden der
PTCDA-Emission werden die Banden des TiOPc-Monomers sichtbar, die
im weiteren in die TiOPc-Kristallemission übergehen.
O 4.2 Mo 11:30 H43
Molecular orientation in perylene thin films on
Al2O3/Ni3Al(111) — •M. B. Casu, A. Schöll, K. R. Bauchspieß,
D. Hübner, Th. Schmidt, C. Heske, and E. Umbach —
Experimentelle Physik II, Universität Würzburg, Am Hubland, 97074
Würzburg
Organic Field Effect Transistors (OFETs) are a rapidly developing field
and many efforts are directed towards their optimisation. We have investigated
thin films of perylene, a model candidate as OFET material, grown
by organic molecular beam deposition (OMBD) on Al203/Ni3Al(111). By
means of Near-Edge X-ray Absorption Fine Structure (NEXAFS), we
studied the influence of the growth parameters on the molecular orientation
and the consequential changes in the electronic fine structure. We
find that it is possible to tailor the molecular orientation of perylene by
using different sets of growth parameters. Thus, it is possible to grow
films in which the chosen molecular orientation is optimal for a charge
transport between source and drain. We also investigated their thermal
stability and their vacuum stability as a function of time (perylene is
characterised by a high vapour pressure). As will be discussed, the overall
results are helpful to understand the interactions between the organic
molecules and the substrate and to answer the question whether perylene
can be used for real OFET devices. (Financed by DFG, SP 1121,
Um 618-2)
O 4.3 Mo 11:45 H43
Growth of para-hexaphenyl microrings — •Frank Balzer 1 and
Horst-Günter Rubahn 2 — 1 Humboldt-Universität zu Berlin, Institut
für Physik / ASP — 2 SDU Odense, Fysisk Institut, Denmark
Recently we have shown, that on freshly cleaved mica the growth of
mutually aligned fibers of para-hexaphenyl is favored because of a dipoleassisted
self-assembly process [1]. Typical heights and widths of these
fibers are in the range of a few ten to hundred nanometers, but lengths
up to one millimeter can be obtained. However, altering the mica surface
dipoles leads to the growth of para-hexaphenyl microrings instead
of parallel fibers. These rings possess a narrow size distribution of a few
micrometers in diameter with wall widths and heights of a few hundred
nanometers. Polarized two-photon luminescence on single rings reveals
that these rings resemble bent single crystalline fibers [2]. Possible applications
of the microrings are discussed.
[1] F. Balzer and H.-G. Rubahn, Appl. Phys. Lett. 79 (2001) 3860.
[2] F. Balzer, J. Beermann, S.I. Bozhevolnyi, A.C. Simonsen, and H.-G.
Rubahn, Nano Letters 3 (2003) 1311.
O 4.4 Mo 12:00 H43
Self-organization of Phthalocyanine films on Al2O3 substrates:
in-plane alignment and ordering — •Esther Barrena 1 , J.Oriol
Ossó 2 , Frank Schreiber 3 , M.Isabel Alonso 2 , Miquel Garriga 2 ,
and Helmut Dosch 1,4 — 1 Max-Planck-Institut für Metallforschung,
Heisenbergstr.3, 70569 Stuttgart, Germany — 2 Institut de Ciència
de Materials de Barcelona CSIC, 08190 Bellaterra, Spain — 3 Physical
and Theoretical Chemistry Laboratory, University of Oxford, Oxford
OX13QZ, UK — 4 Institut für Theoretische und Angewandte Physik,
For the development of organic electronic devices, such as Organic
Field Effect Transistors, the controlled growth of ordered films is prerequisite.
However, it is still challenging to find systems where the balance
between intermolecular forces and interaction with the substrate leads
to the formation of layered films with defined in-plane orientation. In
this work we show that F16CuPc molecules self-organize on Al2O3 (11¯20)
substrates forming unidirectionally oriented needle-like structures. X-ray
diffraction reveals a highly ordered layered structure with the (001) plane
parallel to the surface. The morphology, investigated by Atomic Force Microscopy
(AFM), is smooth and consists of long (microns) and narrow
(tens of nm) needle-like terraces unidirectionally aligned along one of the
main crystallographic directions of the Al2O3 (11¯20) surface. Molecularly
resolved AFM reveal in-plane molecular order with the molecular stacking
parallel to the needle-like terraces. We discuss different mechanisms
leading to this anisotropic structure.
O 4.5 Mo 12:15 H43
Preparation of stacked alkylsiloxane bilayers by spin coating
— •Rafael Bautista, Steffen Franzka, Daniel Dahlhaus, and
Nils Hartmann — Universität Duisburg-Essen, Fachbereich Chemie,
Universitätsstr. 5, 45141 Essen
A simple one-step procedure for the preparation of stacked alkylsiloxane
bilayers is suggested. Solutions of alkyltrichlorosilanes have been spin
coated onto oxidized and H-terminated silicon substrates, respectively.
Subsequently, the samples are inspected by optical and atomic force microscopy.
On the oxidized substrates the coating results in the formation
of macroscopic cellular structures. Whereas, ordinary alkylsiloxane islands
can be identified within the cells, stacked alkylsiloxane bilayers are
formed close to the rim of these structures. In contrast, a macroscopically
more homogeneous coating with stacked alkylsiloxane bilayers results on
the H-terminated substrates. Initially, the bilayers show a remarkable
flexibility. Using the tip of the atomic force microspcope, they can be
easily shifted between the levels maintaining the vertical alignment of
the molecular units. Only after some days, lateral cross-linking appears
to set in.
O 4.6 Mo 12:30 H43
Order and symmetries of sexithiophene within thin films
studied by angle-resolved photoemission — •Cynthia Heiner 1 ,
Bernd Winter 1 , Jens Dreyer 1 , Hans-Hermann Ritze 1 , I.V.
Hertel 1 , and Wolf Widdra 2 — 1 Max-Born-Institut, D-12489 Berlin
— 2 Universität Halle-Wittenberg, D-06099 Halle
We present angle-resolved photoemission (PE) spectra of ordered multilayer
sexithiophene (6T) films, 2000 ˚A thickness, grown on a Au(110)
single crystal. Structural order is crucial for film properties, particularly
with regard to the performance of organic electronic devices. The measurements
were performed at the MBI undulator beamline at BESSY,
using photon energies < 100 eV. By simultaneous laser irradiation a
compensation for film charging is achieved. The resulting spectra possess
sharp features, which we show to have a strong intensity dependency
on the experimental geometry. The molecules’ relative orientation, as interpreted
through symmetry selection rules, is discussed in relation to
various conformers. Our results firmly suggest the need for alternative
molecular symmetries from the reported C2h symmetry for the 6T’s bulkcrystalline
structure [1]. [1] R. N. Marks, M. Muccini, E. Lunedi, R. H.
Michel, M. Murgia, R. Zamboni, C. Taliani, G. Horowitz, F. Garnier, M.
Hopmeier, M. Oestreich, R. F. Mahrt, Chem. Phys. 227, 49 (1998).