Plenarvorträge - DPG-Tagungen

Chemische Physik und Polymerphysik Dienstag
sis) which would provide temporal as well as local information about the
chemical environment if one labels the host (or guest) molecule with an
atomic marker. To this end, we labelled Calixarenes with iodine markers
and attached them to gold substrates with dialkyl-sulfide linkers. The
film stechiometry, thickness and density were studied with XPS, AFM
and imaging ellipsometry, respectively. The results support the expected
elemental composition and a film thickness compatible with the molecular
orientation perpendicular to the surface.
CPP 16.20 Di 17:00 B
Single Molecule Diffusion under Confinement and Shear —
•Arne Schob und Frank Cichos — Institut für Physik 123705, TU
Chemnitz, 09107 Chemnitz
Liquids at solid surfaces may show a completely different structure
compared to the bulk structure, since they may form a layering structure
parallel to the surface. Such a structural difference immediately implies
dynamical differences, which shows up in an anisotropic Brownian motion
or even in a different shear viscosity. An understanding of this behavior is
a key to understand lubrication and friction on a molecular scale. We employ
fluorescent dye molecules to measure molecular mobility in ultrathin
liquid films confined between two atomically flat surfaces. We use highly
doped liquid films to measure the film thickness as a function of applied
force. In this way we are able to calibrate our setup for single molecule
experiments and to compare our results with other publications. Single
molecules are tracked with a wide field fluorescence microscope coupled
to a surface forces apparatus. The experiments show, that corresponding
to measurements on free liquid films the diffusion of molecules is slowed
down due to the interaction with the solid interface. We are further able
to apply shear to the liquid film by moving one of the confining solid surfaces.
By seperating their diffusive motion from the shear-driven motion,
we have acces to the velocity within the sheared liquid on a molecular
scale.
CPP 16.21 Di 17:00 B
Single Molecule Adsorption and Desorption on Solid Surfaces
— •Jörg Schuster 1 , Frank Cichos 2 , and Christian von Borczyskowski
1 — 1 Institut für Physik 121501, TU Chemnitz, 09107
Chemnitz — 2 Institut für Physik 123705, TU Chemnitz, 09107 Chemnitz
Adsorption and desorption are key elements in many processes in physical
chemistry such as self assembly, self organization, surface chemical
reactions or even chromatography. By means of single molecule tracking
in wide field fluorescence microscopy we are able to follow directly the
absorption and desorption of molecules on a solid surface. Experiments
on ultrathin liquid films on solid surfaces show, that the re-adsorption
process of single molecules on the surface is directly influenced by the
reduced film thickness. While the re-adsorption time for a molecule at a
liquid solid boundary is usually expected to follow a power law statistics,
we observe an exponential statistics for liquid films of a few nanometer
thickness. The exponential statistics is the result of the reflection of dye
molecules on the liquid vapor interface. Therefore the mean re-adsorption
time gets finite compared to an infinite time in the bulk and shows further
an exponential tail. The decay time of the exponential tail is directly
related to the film thickness and the diffusion constant perpendicular to
the surface. The measurement of the film thickness and the re-adsorption
statistics thus allows for the first time the determination of the diffusion
constant perpendicular to the surface in a 4 nm film. The experiments
show, that this diffusion is slowed down by 4 orders of magnitude compared
to the in plane diffusion. Thus diffusion in liquid films close to solid
surfaces can be extremely anisotropic.
CPP 16.22 Di 17:00 B
Roughness-Induced Acoustic Second Harmonic Generation
(ASHG) During Electrochemical Metal Deposition on the
Quartz Crystal Microbalance — •Katrin Wondraczek 1 ,
Susanne Wehner 2 , Andreas Bund 2 , and Diethelm Johannsmann
1 — 1 Institut fuer Physikalische Chemie, TU Clausthal,
Arnold-Sommerfeld-Str. 4, D-38678 Clausthal-Zellerfeld — 2 Institut fuer
Physikalische Chemie und Elektrochemie, TU Dresden, Mommsenstrasse
13, D-01062 Dresden
When operating a quartz crystal with a rough surface in liquids, there
is an emission of shear and compressional waves at twice the frequency
of the exciting wave (acoustic second harmonic generation, ASHG). We
used electrochemically deposited copper layers whose roughnesses could
be tuned via current density.
Roughness is a source of ASHG if the liquid flow at the surface is
not entirely laminar. The calculation of the Reynolds number shows that
slight deviations from laminar flow can be reached at high amplitudes of
shear oscillation. However, nonlinear effects in the operation of the QCM
in liquids are small.
Our experiments show that a rough surface is much more efficient
in generating acoustic second harmonic waves than a smooth one. We
present a model that relates ASHG to a roughness parameter independently
obtained from resonance frequency and bandwidth. Such a parameter
allows to distinguish the effects of trapped liquid and hydrodynamics
on rough surfaces from the effects of deposited mass.
CPP 16.23 Di 17:00 B
Phtalocyanines at ZnO-Single Crystals — •Peter Kunze 1 , Malgorzata
Boruszczak 2 , Christine Mattheus 1 , Derck Schlettwein
1 , and Katharina Al-Shamery 1 — 1 Institute of Pure and Applied
Chemistry, Faculty V, University of Oldenburg, Oldenburg, Germany
— 2 Uniwersytet Lodz, Lodz, Poland
The aim of this study is to build up solar cells made of zinc oxide
and organic pigments, especially phthalocyanines and perylenes. This requires
accurate knowledge about the structures and binding between the
Zinc oxide and the organic component. In a UHV-chamber phthalocyanines,
subphthalocyanine and MePTCDI have been deposited onto Zinc
oxide of (0001)- and (10-10)-orientation. UV-VIS measurements reveal
the formation of different film morphologies depending on the different
surface orientations of zinc oxide. RHEED investigations showed no lateral
ordering of the phthalocyanines either at the (0001) or the (10-10)
surface. Additionally AFM measurements have been performed on these
samples. They indicate Vollmer-Weber growth with Islands up to 15nm
height and up to 100nm width at ZnO (0001). At ZnO (10-10) Stranski-
Krastanov-growth is observed with the build up of closed monolayers on
which islands of about 10nm height and up to 40nm width can be found.
None of the phthalocyanines, but PcVO showed lateral ordering in the
RHEED pictures. According to the AFM pictures PcVO showed elongated
islands of about 100nm length and only 10nm width which appear
to be ordered in small domains. Beside domains of different orientations
unordered areas could be seen as well. This supports the results of the
RHEED investigations.
CPP 16.24 Di 17:00 B
Debonding of pressure sensitive adhesives — •E. Maurer 1 , S.
Loi 1 , E. Bauer 1 , T. Mehaddene 1 , S. Cunis 2 , and P. Müller-
Buschbaum 1 — 1 TU München Physik Department LS E13, James-
Franck-Str.1, 85747 Garching — 2 HASLYAB, Notkestr. 85, 22607 Hambung
important class in adhesive technology. Typical examples in daily life
are adhesive stickers, Scotch tape or stick-on notes. Symptomatic for this
kind of adhesives is the dependence of adhesions quality on the bonding
history. Important parameters are contact pressure and contact time. In
most applications of PSA later a controlled debonding of the glued devices
is desired. Despite high technological relevance, the physical mechanism
of adhesion are still not fully understood. In addition the function of
the fibrils appearing during debonding is not sufficiently clear. A macroscopic
understanding of adhesion is provided by the so called tack test.
A cylindrical punch is pressed under defined conditions (contact force,
contact time) onto an adhesive film. While redrawing the punch with
a constant velocity the force is measured. A microscopic investigation
of the adhesion can be achieved by a scattering experiment during the
tack test. We applied small angle x-ray scattering (SAXS). The combination
of both, macroscopic mechanical data and microscopic information,
is a promising attempt on the way to a detailed understanding of the
mechanism underlying adhesion.
CPP 16.25 Di 17:00 B
Ultra-fast calorimetry using thin film sensor — •Sergey
Adamovsky and Christoph Schick — Universitätsplatz,3, 18055,
Rostock, Germany
An application of an ultra-fast thin film calorimeter to polymer materials
is described. A commercially available sensor, thermal conductivity
gauge TCG-3880 (Xensor Integrations, NL) was utilized as a measuring
cell for calorimetric measurements. The sensor consists of a 500-nm
thin SiN membrane with a semiconducting heater and a semiconducting
thermopile, which are produced using integrated-circuit (IC) technology.
To allow fast scanning, sample size should be small too. Samples with
masses of about 100 nanograms were measured.
Heating as well as cooling with rates up to 10,000 K/s were realized.