Hans Martin Sauer

Imaging internal flows in a drying sessile polymer dispersion drop using Spectral Radar Optical Coherence Tomography (SR-OCT)

In this work, we present the visualization of the internal flows in a drying sessile polymer dispersion drop on hydrophilic and hydrophobic surfaces with Spectral Radar Optical Coherence Tomography (SR-OCT). We have found that surface features such as the initial contact angle and pinning of the contact line, play a crucial role on the flow direction and final shape of the dried drop. Moreover, imaging through selection of vertical slices using optical coherence tomography offers a feasible alternative compared to imaging through selection of narrow horizontal slices using confocal microscopy for turbid, barely transparent fluids.

Nanoscaled Nickel-Zinc-Iron Oxides of Spinell Type as Soft Magnetic Colloids and their Ferromagnetic Resonance Spectrum

Summary Colloids made from ferrite nanoparticles are a good example of how the properties of materials change when scaled down to the nanometre scale: the continuous spectrum of magnetic spin wave excitations breaks up to a set of discrete absorption lines. In order to exploit this phenomenon, the chemical composition of the ferrite as well as the preparation method for the suspensions are essential: in nickel zinc ferrites, the magnetic anisotropy field and the life time of magnetic resonance states can be fine tuned by the zinc content to achieve optimal microwave absorption. This makes such colloids interesting for high-power microwave applications, such as bond/disbond-on-command, that are difficult to obtain with polycrystalline materials.

Printing technique dependent charge carrier velocity distribution in organic thin film transistors

In this study we investigated the influence of the deposition technique on the surface topology and the resulting device performance in organic thin film transistors (OTFT). We varied the parameters of flexographic and gravure printing for the organic semiconductor (OSC) and did multilayer gravure printing for the dielectric, respectively. Therefore, we manufactured transistors in bottom contact top gate architecture and compared them to spin coated samples. As investigation tool for OTFTs, the charge carrier velocity distribution is correlated with the optical characteristics of the printed layers. We found a dependency of the printing technique on the surface topology of the semiconductor and, due to the resulting increase of the channel length, a broadening of the charge carrier velocity distribution. For the dielectric we found a dependency on the layer thickness which seems to be independent from the deposition technique.

Improved contact resistivity and intra-die variation in organic thin film transistors

We studied the processing-related influence on contact resistivity of organic thin-film transistors in top gate architecture which are placed and oriented differently over flexible substrates. Appropriate plasma treatment reduces degradation of the source and drain contacts, increases effective contact surface for self-assembled monolayer treatment, and thus better injection. Increasing the semiconductor film thickness reduces the contact resistivity until a certain critical thickness. By these means, the contact resistivity has been reduced by two orders of magnitude. We did a mass characterisation of 366 solution-processed transistors on six samples that lead to a modified transfer line method in which we permutated the transistors to extract the contact resistivities. Thus, the intra-die dependency of the contact resistivity on the distance from the centre of the sample, the orientation of the transistor, its width, the pre-processing of the samples and on the semiconductor layer thickness has been ana...

Beschleunigte Klebstoffhärtung mit Mikrowellen und Nanoferriten

Zur raschen Hartung von Reaktivklebstoffen wird gelegentlich die Bestrahlung mit Mikrowellen vorgeschlagen. Neben den bekannten Vorteilen wie dem hohen Energiewirkungsgrad und der Vertraglichkeit mit modernen Leichtbaumaterialien gibt es aber auch gewichtige Hurden: Wie sieht ein geeigneter Klebprozess aus? Wie stellt man eine gleichmasige Hartung sicher? Woher bezieht man spezifizierte Klebstoffe und Fertigungsanlagen? Auf der Basis von nanoskaligen Eisenoxiden wurde ein neues Klebsystem entwickelt, das sowohl die Bereitstellung geeigneter Klebstoffadditive als auch die Anlagentechnik umfasst.