Plenarvorträge - DPG-Tagungen
Plenarvorträge - DPG-Tagungen
Plenarvorträge - DPG-Tagungen
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
Symposium Organic and Hybrid Systems for Future Electronics Donnerstag<br />
SYOH 4 Hybrid Systems and Devices<br />
Zeit: Donnerstag 16:45–17:45 Raum: H37<br />
SYOH 4.1 Do 16:45 H37<br />
Fast integrated plastic circuits — •Robert Blache, Andreas<br />
Ullmann, Jürgen Ficker, Dietmar Zipperer, Walt e r Fix, and<br />
Wolfgang Clemens — PolyIC GmbH & Co. KG, Paul-Gossen-Str.<br />
100, 91052 Erlangen, Germany<br />
Using soluble polymers as active and insulating layers we report on<br />
fast and stable integrated circuits based on p-type organic transistors.<br />
On flexible polyester film substrates single field-effect transistors and ring<br />
oscillators with frequencies above 190 kHz and propagation stage delays<br />
below 0.4 µs were fabricated with regioregular poly(3-alkylthiophene).<br />
Even without encapsulation the devices show a very stable performance<br />
while stored and measured under ambient and extreme conditions<br />
[1]. Furthermore we report on organic rectifiers based on polymer<br />
rectifier diodes and polymer capacitors. Our results show the potential<br />
of integrated plastic circuits based on soluble polymers to be suitable<br />
for inexpensive high volume electronic applications (e.g. RFID-tags).<br />
[1] J. Ficker, et al., JAP 2003, Vol.94, p. 2638<br />
SYOH 4.2 Do 17:00 H37<br />
Submicron Polymer Field-Effect Transistors — •Susanne<br />
Scheinert 1 , Axel Scherer 2 , Theodor Doll 1 , Gernot Paasch 3 ,<br />
and Ingo Hörselmann 1 — 1 TU Ilmenau — 2 CALTECH, Pasadena,<br />
USA — 3 IFW Dresden<br />
Application-relevant speed of polymerelectronics requires transistors<br />
with submicrometer channel length. At present appropriate low-cost<br />
patterning does not exist. We prepared such transistors using a nonlithographic<br />
technique for the definition of the channel length in the<br />
submicron range. To avoid short-channel effects a hybrid design with<br />
silicon dioxide as gate insulator is used. As active layer different poly(3alkythiophene)<br />
(P3AT) has been used. The transistors feature (i) controlled<br />
defined channel length between 0.75µm and 1µm, (ii) an operation<br />
at voltages lower than 5V , (iii) well pronounced saturation of<br />
the output characteristics with (iv) only marginal short channel effects,<br />
(v) a high on-off ratio (> 10 4 ), (vi) rather small inverse subthreshold<br />
slope S ≈ 0.5V/dec, and (vii) negligible contact resistances. Since<br />
the used P3AT were not especially treated, the mobility is still low<br />
(≈ 2...3cm 2 /V s). The hysteresis is negligible for the drain voltage sweep<br />
for a given gate voltage, but as usual there is a hysteresis for the gate voltage<br />
sweep at given drain voltage. However, the corresponding threshold<br />
voltage shift is with ≈ 1V relatively small.<br />
SYOH 5 Poster<br />
SYOH 4.3 Do 17:15 H37<br />
Cascade energy transfer in bandgap modulated multilayer<br />
structures of CdTe quantum dots — •Thomas Franzl, Stefan<br />
Schietinger, Thomas A. Klar, Andrey L. Rogach, and<br />
Jochen Feldmann — Photonics and Optoelectronics Group, Physics<br />
Department and CeNS, Ludwig-Maximilians-Universität München,<br />
Amalienstr. 54, D-80799 Munich, Germany<br />
We report on very fast and directed energy transfer leading to<br />
strongly increased excitonic densities in cascaded energy transfer structures<br />
(CET) made of CdTe quantum dots capped by short chain thiols.<br />
A systematic bandgap variation in one spatial direction is realized by<br />
a layer-by-layer technique using CdTe nanocrystals of stepwise increasing<br />
sizes in subsequent layers. We observe an efficient energy transfer<br />
towards the layer of largest quantum dots. In this layer the excitonic<br />
density increases by an order of magnitude in comparison to a layered system<br />
containing only one size of CdTe nanocrystals. These high excitonic<br />
densities in CET structures are especially interesting for optoelectronic<br />
devices such as nanocrystal LEDs or lasers.<br />
SYOH 4.4 Do 17:30 H37<br />
Optical modeling of CuPc/C60 photovoltaic devices — •T.<br />
Stübinger 1 and W. Brütting 2 — 1 Experimentalphysik II, Universität<br />
Bayreuth, D-95440 Bayreuth — 2 Experimentalphysik IV,<br />
Universität Augsburg, D-86135 Augsburg<br />
Photovoltaic devices with Cu-phthalocy anine (CuPc) as electron<br />
donor and Buckminsterfullerene (C60) as electron acceptor exhibit high<br />
incident photon-to-current conversion efficiencies (IPCE) in bilayer devices<br />
and composite systems. Optical interference effects significantly influence<br />
photocurrent spectra and quantum efficiencies, which arises from<br />
the strong dependence of layer thicknesses on the spatial distribution of<br />
the photon density. By optical modelling using transfer-matrix-methods<br />
the experimental photocurrent spectra of bilayer systems with various<br />
layer thicknesses (organic layers, buffer layers, electrodes) could be explained.<br />
Blend systems of CuPc and C60 show high quantum efficiencies<br />
of almost 60% (IPCE) due to an effectively enhanced dissociation volume<br />
in these composite systems. These high IPCE values demonstrate a<br />
very efficient photocarrier generation and charge transport in these low<br />
molecular weight composite systems, which is comparable to the most<br />
efficient polymer-fullerene composite systems after post-annealing treatments.<br />
The mixing ratio and total layer thickness of the blend system<br />
are varied to achieve optimum photovoltaic performance.<br />
Zeit: Donnerstag 18:00–21:00 Raum: B<br />
SYOH 5.1 Do 18:00 B<br />
Normal Incidence X-ray Standing Waves on Light Elements:<br />
The Limits of the Dipole Approximation — •Christian Kumpf,<br />
Jörg Stanzel, Christoph Stadler, Wolfgang Weigand, and<br />
Eberhard Umbach — Experimentelle Physik II, Univ. Würzburg<br />
The normal incidence x-ray standing wave (NIXSW) technique is a<br />
powerful tool for obtaining detailed structural information on surfaces,<br />
e.g., exact atomic coordinates which enable quantum chemical calculations.<br />
In most XSW experiments either the photoelectron or the Augerelectron<br />
yield is used to measure the absorption of a specific atomic<br />
species adsorbed on a surface. For the analysis of organic adsorbates,<br />
which contain low-Z elements only, this is a difficult issue since the dipoleapproximation<br />
is no longer sufficient to describe the photoemission process.<br />
Using the Auger yield is also problematic since the Auger process is<br />
not only stimulated by the x-ray standing wave field but also by (photo-)<br />
electrons emerging from the bulk. Therefore, significant effort was put in<br />
finding a proper way to correct the photoemission yield for non-dipolar<br />
contributions as well as the Auger-yield for its electron-induced portion.<br />
We report on a NIXSW experiment performed on a coherent monolayer<br />
of NTCDA on Ag(111) for which this correction was successfully<br />
performed and consistent results were obtained from the O1s photo electron<br />
yield as well as from the OKLL Auger electron yield. The electroninduced<br />
portion of the Auger yield was found to be as large as 50%.<br />
Furthermore, a significant covalent character was found for the bonding<br />
between the NTCDA molecules and the substrate. The bonding distance<br />
is 3.08(3)˚A, considerably smaller than a Van der Waals distance.<br />
SYOH 5.2 Do 18:00 B<br />
Template guided self-assembly of nanoclusters — •Li Zhang,<br />
Lifeng Chi, and Harald Fuchs — Physikalisches Institut,<br />
Westfälische Wilhelms-Universität, Wilhelm-Klemm-Str. 10, 48149<br />
Münster, Germany<br />
Surface patterning with microscopically small structures has attracted<br />
increasing scientific and technological interest over the past decade. In<br />
our work, variable surface patterns of chiral molecule C11-CO-(L)-Cys-<br />
(L)-Cys-NH-C18 are obtained by changing the subphase conditions. At<br />
the air- water (pure) interface, it forms a kind of chiral pattern. Due<br />
to the potential complex ability of the sulfur atom in the molecule, this<br />
kind of surface aggregate could be used as a template to trap the metal<br />
ions or nanoparticles during its interfacial assembly process, which may<br />
provide a method to assemble the metal or semi-conductor particles into<br />
a designed way.<br />
Using the metal ions as subphase, the chiral pattern size is smaller compared<br />
with the result without metal ions. The size of this kind of aggregate<br />
decreases with increased concentration of metal ions. For the subtle<br />
structure inside the circle domain, the stripe like structure is found. At<br />
the air-CdTe nanoparticle aqueous interface, a kind of branched nanostripes<br />
appears. The furcation point appears at the end of some branches.