Plenarvorträge - DPG-Tagungen

Oberflächenphysik Montag
O 14.60 Mo 18:00 Bereich C
Intermolecular Interactions in Thin Films of SubphthalocyaninatoChloroBoron
(SubPc) and its Fluorinated Derivative
(F12SubPc) — •Christine Mattheus 1 , Dieter Wöhrle 2 ,
William Durfee 3 , and Derck Schlettwein 1 — 1 Physical
Chemistry 1, University of Oldenburg, Germany — 2 Institute of Organic
and Macromolecular Chemistry, University of Bremen, Germany —
3 Department of Chemistry, Buffalo State College, NY, USA
Thin films of unsusbstituted SubPc and perfluorinated F12SubPc were
prepared by PVD on various single crystalline and amorphous insulators.
The intermolecular coupling was studied by in situ UV- vis absorption
spectroscopy, the morphology was analysed by atomic force microscopy
(AFM) and the structure of the films was studied by X-ray diffraction
(XRD). For SubPc, a rather small influence of the substrate structure
was observed, whereas F12SubPc showed significantly different spectra
on KBr and KCl when compared to NaCl, mica or glass. For both materials,
spectral characteristics were observed that point at changing interactions
of the molecules in the solid films. In the AFM analysis larger
and more oriented grains were found for films grown at elevated temperature.
These films were characterized by well- defined chromophores
coupling as seen in UV-vis spectroscopy and were crystalline as observed
in XRD. Relative intensities in XRD were used to discuss a preferential
orientation of crystals and hence the molecules relative to the surface.
O 14.61 Mo 18:00 Bereich C
Surface photovoltage of thin organic layers on single-crystal
metal and semiconductor surfaces — •Sebastian Teich, Stefan
Grafström, Christian Loppacher, Ulrich Zerweck, and
Lukas Eng — Institute of Applied Photophysics, University of Technology
Dresden
Surface photovoltage (SPV) investigations of ultrathin organic films
on metal and semiconductor substrates with a unique sensitivity of
< 1 mV are reported. This is achieved with a novel phase-sensitive
method based on an accurate measurement of the light-induced shift
of the ultraviolet (UPS) or x-ray (XPS) photoemission spectrum under
power-modulated illumination of the sample. Furthermore, in order
to derive local SPV information with high spatial resolution, we
use similar modulation methods, however involving scanning tunneling
and atomic force microscopy rather than XPS/UPS. Our SPV
studies provide access to electronic properties of semiconductor surfaces
and interfaces, including in particular organic-inorganic interfaces.
We demonstrate the versatility of our SPV techniques for thin films
of perylene-tetracarboxylic dianhydride (PTCDA) and Cu-tetra-3,5 ditertiary-butyl-phenyl
porphyrin (Cu-TBPP) on various substrates, including
Cu(100) and Ge(100).
O 14.62 Mo 18:00 Bereich C
Deposition of ordered TiOPc thin films by Supersonic Molecular
Beam Epitaxy (SuMBE) — •Karsten Walzer 1 , Tullio
Toccoli 2 , Alessia Pallaoro 2 , Roberto Verucchi 2 , Salvatore
Iannotta 2 , Torsten Fritz 1 , and Karl Leo 1 — 1 Institut für Angewandte
Photophysik, TU Dresden, 01062 Dresden, Germany — 2 Institute
for Photonics and Nanotechnology, Trento, Italy
The deposition of organic thin films for device applications requires a
reliable method for the deposition of well-ordered molecular films significantly
above the monolayer level. Searching for an alternative method to
conventional organic molecular beam deposition (OMBD), we used Supersonic
Molecular Beam Epitaxy (SuMBE) for the deposition of ordered
organic films. The method uses the expansion of an inert carrier gas into
vacuum with organic molecules seeded into the beam, which allows to
control both energy and momentum of the molecules.
We present the SuMBE growth of titanyl phthalocyanine (TiOPc),
which is of interest for organic solar cells. Substrates were glass and mica.
Depending on substrate and substrate temperature we could adjust the
growth of different crystal phases and surface morphologies. Especially
the TiOPc phase II was grown at significantly lower substrate temperatures
than usually needed in OMBD.
O 14.63 Mo 18:00 Bereich C
Inital growth of PTCDA on Cu(100) investigated by STM —
•Thorsten Wagner, Christian Bobisch, Amin Bannani, Hatice
Karacuban und Rolf Möller — Universtität Duisburg-Essen,
Institut für Experimentelle Physik, Universitätsstr. 3-5, 45141 Essen
The organic semiconductor 3,4,9,10-perylene-tetracarboxylic-
dianhydrid (PTCDA) has been subject of many investigations. In this
work we will discuss the initial growth of PTCDA on a Cu(100) single
crystal surface. The investigations have been carried out with a self
build STM under UHV conditions. The films with a thickness of about
one monolayer have been grown by means of thermal evaporation from a
heated crucible. A structure comparable to the square phase also found
by Chizhov et al. on Au(111. The growth of PTCDA on Cu(100) will be
compared to results on other copper surfaces.
[1] I. Chizhov et al., Journal of Crystal Growth 208 (2000) 449-458
O 14.64 Mo 18:00 Bereich C
STM investigations of very large macrocycles adsorbed on
surfaces — •Iordan Kossev and Moritz Sokolowski — Institut
für Physikalische und Theoretische Chemie, Universität Bonn, Wegelerstr.
12, 53115 Bonn, Germany
Rotaxanes and catenanes are of interest for the investigation on mechanically
interlocked molecules [1]. A large tetralactam - macrocycle
(961.3 amu), used as a building block for rotaxanes and catenanes, was
deposited onto the Au(111) surface from a thermal evaporation cell. STM
images were taken for different coverages at room temperature. At a coverage
of less than one monolayer, it was found that the macrocycles form
small clusters at step edges and surface defects, leaving large terraces
uncovered. At a coverage around one monolayer, the molecules form disordered
structures, which remain disordered after annealing to 423 K.
Presumably, the reason for these observations is the week interaction between
the Au surface and the molecules, in combination with a strong
hydrogen – bonding between the molecules. Further investigations on the
ordering of these molecules on more reactive surfaces like Ag(111) and
Cu(111) are under progress. The macrocycles were kindly supplied by
C. Schalley and F. Vögtle. This work was supported by the DFG (SFB
624). [1] J.-P. Sauvage, Acc. Chem. Res. 31, (1998) 611.
O 14.65 Mo 18:00 Bereich C
Untersuchung von Punkt- und Liniendefekten auf der
NiO(001)-Spaltfläche mittels Rasterkraftmikroskopie — •Nico
Plock, U. Kaiser, A. Schwarz und R. Wiesendanger — IAP,
Mikrostrukturzentrum, Universität Hamburg
Die Übergangsmetalloxide, zu denen auch NiO gehört, waren vor allem
aufgrund ihrer katalytischen Eigenschaften in der Vergangenheit bereits
Gegenstand zahlreicher Untersuchungen. NiO zeigt bei defektfreien
Oberflächen kaum reaktives Verhalten, während z.B. durch Punkt- und
Liniendefekte die Reaktivität stark gesteigert wird. Wir haben mittels eines
Rasterkraftmikroskops (RKM) im Ultrahochvakuum Untersuchungen
an in situ-präparierten (001)-Oberflächen von NiO durchgeführt. Dazu
wurden verschiedene Proben nach dem in situ-Spalten mit dem RKM
abgebildet und anschließend für acht bis zwölf Stunden auf Temperaturen
zwischen 200 ◦ C und 720 ◦ C geheizt. Anschließend wurden die Proben
mit LEED und Augerspektroskopie, sowie dem RKM untersucht. Neben
Ladungen und Adsorbaten auf der Oberfläche wurden sowohl Fehlstellen
als auch Linien- und Punktdefekte gefunden.
O 14.66 Mo 18:00 Bereich C
First-principles study of Cu interacting with polar ZnO surfaces
— •Bernd Meyer and Dominik Marx — Lehrstuhl für Theoretische
Chemie, Ruhr-Universität Bochum, D-44780 Bochum, Germany
The structure and electronic properties of single Cu atoms, copper
monolayers and thin copper films on the polar oxygen and zinc terminated
surfaces of ZnO are studied using periodic density–functional
calculations. We find that the binding energy of Cu atoms sensitively depends
on how charge neutrality of the polar surfaces is achieved. Bonding
is very strong if the surfaces are stabilized by an electronic mechanism
which leads to partially filled surface bands. As soon as the surface bands
are filled (either by partial Cu coverage, by coadsorbates, or by the formation
of defects), the binding energy decreases significantly. In this case,
values very similar to those found for nonpolar surfaces and for copper
on finite ZnO clusters are obtained. Possible implications of these observations
concerning the growth mode of copper on polar ZnO surfaces and
their importance in catalysis are discussed.
O 14.67 Mo 18:00 Bereich C
Valence Band Spectroscopy on CoO Surfaces: A Comparison of
MIES and UPS(HeI) Results — •F. Schweiger, S. Rudenkiy,
M. Frerichs, W. Maus-Friedrichs, and V. Kempter — Institut
für Physik und Physikalische Technologien, Technische Universität
Clausthal, D–38678 Clausthal–Zellerfeld, Germany