TY  - GEN
ID  - heidok19776
AV  - public
CY  - Heidelberg
TI  - Work Function Tuning at Interfaces by Monomolecular Films
Y1  - 2015///
N2  - The control over the work function of surfaces and interfaces is one of the most
important issues of modern surface science and nanotechnology, e.g. in context
of organic electronics and photovoltaics. The goal of this work was to look for
new ways to control the work function of metal substrates by using molecular
self-assembly. Two different strategies were used. The first strategy was to use
aliphatic and aromatic molecules which contain an embedded dipolar group (midchain
functionalization). Such self-assembled monolayers (SAMs) allow for tuning
the substrate work function in a controlled manner, independent of the docking
chemistry and, most importantly, without modifying the SAM-ambient interface.
In the case of aliphatic films, we used alkanethiols functionalized with an embedded
ester dipole, with the length of both top and bottom segments as well as the
direction of the embedded dipole being varied. In the case of aromatic systems, we
used terphenyl based thiols functionalized with an embedded pyrimidine dipolar
group, with the direction of the dipole being varied. The electronic and structural
properties of these embedded-dipole SAMs were thoroughly analyzed using
a number of complementary characterization techniques combined with quantummechanical
modeling. It is shown that such mid-chain-substituted monolayers
are highly interesting from both fundamental and application viewpoints, as the
dipolar groups are found to induce a potential discontinuity inside the monolayer,
electrostatically shifting the core-level energies in the regions above and below the
dipoles relative to one another. Particularly imptortant, in context of the present
work, is the fact that the mid-chain functionalized films are indeed well suited to
adjust the work function of metal substrates. This could be e.g. done by varying
the orientation of the dipolar group but also by mixing the molecules with
differently oriented dipoles as was demonstrated in the present work. Within the
second strategy, we used photoresponsive systems, viz. azobenzene substituted
alkanethiols, having a specially designed architecture to control the packing density
and carrying an additional dipolar tail group. These novel SAMs were studied
in detail by using spectroscopic and microscopic techniques. Performing photoisomerization
experiments we obtained a reproducible, stimuli-responsive change in
the work function which was, however, limited to some extent due to the strong
steric hindrance effects. In order to reduce these effects, we diluted the azobenzene
molecules with short spacer molecules, which resulted in an improvement in the
photoswitching behavior.
A1  - Schuster, Swen
UR  - https://archiv.ub.uni-heidelberg.de/volltextserver/19776/
ER  -