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Plenarvorträge - DPG-Tagungen

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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.

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