Home » Research » Metal Surfaces » Self Assembly
molecular nanostructures and self-assembly – structure
and dynamics
Thomas Waldmann, Michael
Roos, Achim Breitruck, Harry E. Hoster, R. Jürgen Behm
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Physical
background of the self assembly of large organic molecules:
molecule: 2-phenyl-4,6-bis(6(pyrid-2-yl)-4(pyrid-4-yl)pyrid-2-yl)pyrimidine oligopyridine (2,4’-BTP) (Ziener
et al.)
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Molecular nanostructuring plays an important role in today's
research, due to the great possibilities arising from this powerful
technique. The main advantage herein is the ability to steer the
self-organization process into desired nanostructures by use of special
designed molecular building blocks. A major goal of our group is a basic and
comprehensive understanding of molecular self-assembly on well defined
surfaces. Therefore, we investigate the influence of both, the molecule
geometry and its chemical structure on the resulting self-assembled-monolayer
(SAM), as well as the role of the substrate type. By additionally studying
dynamic effects, e.g. the change of domain walls occurring during phase transformations, we are able to describe the
self-organization process quantitatively. A second aim of our team is to use
these SAM's as template for metal incorporation, in
order to perform in a second step model catalytic reactions
at these surfaces. |
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most stable
hydrogen bonds of 2,4’-BTP
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experimental setup
Our experiments are carried
out in an ultra high vacuum (UHV) chamber, equipped with a LEED (low energy
electron diffraction), an AES (Auger electron spectroscopy), a QMS (quadrupol mass spectrometry) and a homebuild
STM (scanning tunneling microscopy) for analysis,
as well as a sputter gun and several evaporators for sample preparation |
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hydrogen bonds visualized in a
Monte-Carlo simulation
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typical hydrogen bonded structures
High resolution STM
pictures of two different phases formed by 2,4'-BTP on Ag(111); coverage
dependent structures results from subtle balance of molecule-molecule and
molecule-substrate interactions |
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molecule - substrate interactions are
dominated by the nitrogen atoms
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thermal desorption: dominance of the
pre-exponential factor
Desorption
from BTP monolayer films occurs at much higher temperatures than fro multilayers.
Surprisingly, the main reason for that is a decrease in the pre-exponential
factor by 9 orders of magnitude,
whereas the energetic desorption barrier remains virtually unchanged
"Entropic stabilization of large
adsorbates on weakly binding substrates – a thermal desorption and scanning tunneling microscopy study", PCCP communications,
in press
dynamics: real time observation of a mobile
phase boundary by Video-STM
phase boundary:
low density quasi-hexagonal phase (partially mobile) and quasi quadratic
network
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see: T. Waldmann, R.
Reichert, H. Hoster, ChemPhysChem, in press |
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