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Klumbies H.,TU Dresden | Muller-Meskamp L.,TU Dresden | Monch T.,TU Dresden | Schubert S.,TU Dresden | And 2 more authors.
Review of Scientific Instruments | Year: 2013

The reaction of calcium thin films with water - monitored optically or electrically - is widely used for evaluating ultrahigh barrier foils for the encapsulation of organic electronic devices. We studied the common optical and the electrical method and compared them with in situ atomic force microscope topography scans. All three methods were applied at the same sample in parallel in a typical test design containing a gas volume for water distribution next to the calcium layer of 60 and 1000 nm thickness, respectively. The common assumption for the interpretation of such measurement data is laterally homogeneous calcium consumption of the layer from top to bottom. In contrast, we observed a significant ratio of laterally inhomogeneous corrosion of the calcium on the micro-scale for both thicknesses. Some areas were strongly or completely corroded through the whole layer while others exhibited less or no corrosion. Furthermore, those corroded spots grew in lateral direction. As a consequence of lateral inhomogeneous calcium corrosion the electrical calcium measurement method underestimates the amount of calcium left; according to our results this does not affect the water vapor transmission rate (WVTR). Optical data evaluated by Lambert-Beer law underestimate the amount of calcium left as well and also underestimate the WVTR. If the data are evaluated, using a linear relationship between transmission and amount of calcium left, the both values are more precise. The scope of this study is to call attention to the existence of lateral inhomogeneity in calcium corrosion and its impact on the calcium permeation measurements. While more investigations would be needed to quantify the effect of this inhomogeneity on the electrical and optical method in general, the discussion sheds light on the way, calcium test data are influenced by lateral inhomogeneous calcium corrosion. Our observations highlight the need for careful interpretation of calcium test results, but also demonstrate its capabilities for precise ultrahigh barrier measurements. © 2013 American Institute of Physics. Source


Schuchert T.,Fraunhofer Institute for Optronics, System Technologies and Image Exploitation | Voth S.,Fraunhofer Institute for Optronics, System Technologies and Image Exploitation | Baumgarten J.,Fraunhofer Institute for Organics, Materials and Electronic Devices
Proceedings of the 4th Workshop on Eye Gaze in Intelligent Human Machine Interaction, Gaze-In 2012 | Year: 2012

This paper presents a novel system for sensing of attentional behavior in Augmented Reality (AR) environments by analyzing eye movement. The system is based on light weight head mounted optical see-through glasses containing bidirectional microdisplays, which allow displaying images and eye tracking on a single chip. The sensing and interaction application has been developed in the European project ARtSENSE in order to (1) detect museum visitors attention/interest in artworks as well as in presented AR content, (2) present appropriate personalized information based on the detected attention as augmented overlays, and (3) allow museum visitors gaze-based interaction with the system or the AR content. In this paper we present a novel algorithm for pupil estimation in low resolution eye-tracking images and show first results on attention estimation by eye movement analysis and interaction with the system by gaze. © 2012 ACM. Source


Schwab T.,TU Dresden | Fuchs C.,TU Dresden | Scholz R.,TU Dresden | Zakhidov A.,Fraunhofer Institute for Organics, Materials and Electronic Devices | And 3 more authors.
Optics Express | Year: 2014

Bragg scattering at one-dimensional corrugated substrates allows to improve the light outcoupling from top-emitting organic light-emitting diodes (OLEDs). The OLEDs rely on a highly efficient phosphorescent pin stack and contain metal electrodes that introduce pronounced microcavity effects. A corrugated photoresist layer underneath the bottom electrode introduces light scattering. Compared to optically optimized reference OLEDs without the corrugated substrate, the corrugation increases light outcoupling efficiency but does not adversely affect the electrical properties of the devices. The external quantum efficiency (EQE) is increased from 15 % for an optimized planar layer structure to 17.5 % for a corrugated OLED with a grating period of 1.0 μm and a modulation depth of about 70 nm. Detailed analysis and optical modeling of the angular resolved emission spectra of the OLEDs provide evidence for Bragg scattering of waveguided and surface plasmon modes that are normally confined within the OLED stack into the air-cone. We observe constructive and destructive interference between these scattered modes and the radiative cavity mode. This interference is quantitatively described by a complex summation of Lorentz-like resonances. © 2014 Optical Society of America. Source


Schwab T.,TU Dresden | Schubert S.,TU Dresden | Hofmann S.,TU Dresden | Frobel M.,TU Dresden | And 5 more authors.
Advanced Optical Materials | Year: 2013

An ultra-thin MoO3-Au-Ag wetting layer metal electrode is investigated to eliminate present optical and electrical limitations of inverted top-emitting OLEDs. Its high transmittance suppresses microcavity effects and the MoO3 hole injection layer compensates limited charge injection from the top contact. Overall, an extensive approach is presented to solve the key problems of top-emitting OLEDs in general. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Hein M.P.,TU Dresden | Zakhidov A.A.,Fraunhofer Institute for Organics, Materials and Electronic Devices | Lussem B.,TU Dresden | Jankowski J.,TU Dresden | And 5 more authors.
Applied Physics Letters | Year: 2014

The key active devices of future organic electronic circuits are organic thin film transistors (OTFTs). Reliability of OTFTs remains one of the most challenging obstacles to be overcome for broad commercial applications. In particular, bias stress was identified as the key instability under operation for numerous OTFT devices and interfaces. Despite a multitude of experimental observations, a comprehensive mechanism describing this behavior is still missing. Furthermore, controlled methods to overcome these instabilities are so far lacking. Here, we present the approach to control and significantly alleviate the bias stress effect by using molecular doping at low concentrations. For pentacene and silicon oxide as gate oxide, we are able to reduce the time constant of degradation by three orders of magnitude. The effect of molecular doping on the bias stress behavior is explained in terms of the shift of Fermi Level and, thus, exponentially reduced proton generation at the pentacene/oxide interface. © 2014 AIP Publishing LLC. Source

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