@inproceedings{MuellerBurkovSchmeisser, author = {M{\"u}ller, Klaus and Burkov, Yevgen and Schmeißer, Dieter}, title = {Spectromicroscopic Characterisation of All Polymer Transistor Structures}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {In order to optimize organic field effect transistors, the characterization of surfaces in terms of their roughness or chemical composition is very important. We report on high resolution spectromicroscopic mapping of organic thin film transistors by photoemission electron microscopy (PEEM). It was shown that PEEM is a useful technique to characterize the surface morphology (roughness), the chemical homogeneity or the composition of structures in between the source and drain electrodes. Mapping of surface potentials, especially at the interface electrode/channel is possible. We compare different preparation methods and the characterization at applied voltages is also shown. The transistors itself were prepared by a new low cost method. The electrodes for source and drain have been prepared by a plotting method with colloidal graphite or carbon black as the conducting material. P3HT was used as active layer and has been prepared by spin coating.}, language = {en} } @inproceedings{MuellerPaloumpaSchwiertzetal., author = {M{\"u}ller, Klaus and Paloumpa, Ioanna and Schwiertz, Carola and Jahnke, Agnes and Schmeißer, Dieter}, title = {All Polymer Field-Effect-Transistors based on Low-Cost-Microstructuring}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {Thin film transistors with P3HT as active layer have been prepared by spin coating. The electrodes for source and drain have been prepared by a low cost plotting method with colloidal graphite or carbon black as the conducting material. PEDOT or carbon black was used as gate electrode. The devices, prepared by different methods and materials have been characterized by electrical measurements, for example, their transfer and output characteristics. Furthermore, the influence of different materials on effects like hysteresis or reproducibility will be compared. In addition, we describe a project investigating new types of biosensors with functionalized gate electrodes. Exchanges of dipole moments or charges by immobilisation of biomolecules will change the electrical characteristic of the transistor, which leads to a sensing signal proportional to their amount.}, language = {en} } @inproceedings{TorcheMuellerHenkeletal., author = {Torche, Mohamed and M{\"u}ller, Klaus and Henkel, Karsten and Lupina, Grzegorz and Goryako, Andrey and Wollweber, J{\"u}rgen and Schmeißer, Dieter}, title = {Investigations of 3C-SiC growth on Si (001)}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {Carbide was grown on Si (001) - substrates with supply of C2H2. Investigation of the interface Si/SiC (buffer layer) is essential for optimized preparation conditions, leading to a high quality of the growing SiC crystal. In addition to the lattice mismatch of 20 per cent between Si and SiC, which causes defects like dislocations or stacking faults, the chemical homogeneity of this layer is important. XPS was used to characterize the first state of SiC crystal growth on the Si substrate. Carbonizing with C2H2 leads to surface reactions which build up the buffer layer. By using electron spectroscopy, it was possible to characterize the SiC/Si (001) buffer layer, depending on the following reaction parameters: Tsubstrate , PC2H2 , PH2 , the ratio of pressures and the reaction time. The measurements were performed in terms of the content of carbide, oxide and roughness/etching-efficiency (Profilometer) for the reaction parameters above. We found, that the most critical parameter is the temperature of the substrate (Tsubstrate).}, language = {en} } @inproceedings{MuellerSchmeisser, author = {M{\"u}ller, Klaus and Schmeißer, Dieter}, title = {Elektronenspektroskopie an Kupferindiumdisulfid Oberfl{\"a}chen}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {In diesem Beitrag wird eine Studie vorgestellt, welche die elektronenspektroskopische Untersuchung von CIS-Oberfl{\"a}chen f{\"u}r Solarzellen zum Thema hatte. XPS-UPS Analysen von Cu-reichen CuInS2-D{\"u}nnfilmen zeigten, daß die Variationen der Elementverh{\"a}ltnisse im Verlauf eines kontrollierten Heizprozesses entlang bin{\"a}rer Schnitte des tern{\"a}ren Phasendiagramms Cu-In-S verlaufen. Die Elementverh{\"a}ltnisse bei zus{\"a}tzlich aufgedampftem Kupfer und erh{\"o}hter Temperatur f{\"o}hrten in den Homgenit{\"a}tsbereich von CuInS2. PEEM-Untersuchungen zur Probenmorphologie zeigten, daß ein Sinterprozess w{\"a}hrend der Temperung der Proben bis 550 C und einer Belegung mit Kupfer erfolgt. Mit Differenz-PEEM-Aufnahmen konnten kupferreiche Fremdphasen wie CuS an der Oberfl{\"a}che sichtbar gemacht werden. Die in-situ Charakterisierung des Oberfl{\"a}chenchemismus im Verlauf der Temperung zeigte eine zunehmende Homgenit{\"a}t der Elementverteilung, was auf einen geringer werdenden Anteil von Fremdphasen hindeutet. NEXAFS-Aufnahmen ergaben erstmals Informationen {\"u}ber die Bandstruktur oberhalb der Fermienergie und ebenfalls Hinweise auf Fremdphasen sowie deren Reaktionen bei h{\"o}heren Temperaturen.}, language = {de} } @inproceedings{HenkelPaloumpaMuelleretal., author = {Henkel, Karsten and Paloumpa, Ioanna and M{\"u}ller, Klaus and Schmeißer, Dieter}, title = {P(VDF/TrFE) as a ferroelectric dielectric for Organic Field effect Transistors in MFIS structure}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {MFIS structures consisting of metal, ferroelectric poly[vinylidene fluoride trifluoroethylene](P[VDF/TrFE]), insulator, semiconductor (Si) are fabricated and the influence of the polarization of the P(VDF/TrFE) on the CV characteristics of these structures is investigated. We find a characteristic ferroelectric hysteresis in the CV curves upon increasing the voltage scan window (e.g.-U...U,U=6...30V, |UP(VDF/TrFE)|≤15V, dP(VDF/TrFE)=300 nm). A writing process with adequate electric fields causes large shifts in the flatband voltage ( Δ UFB>4V for the quoted example before) which are stable over days. We report on our investigations which focus on the switching behavior by varying the parameters like polymer thickness, writing field strength and time, long time stability, reversing voltage and insulating material (SiO2, PMMA (Polymethylmetacrylate)). This material combination is favorable for transfer into our full organic concept of field effect transistors for application as a nondestructive readout memory (NDRO) cell.}, language = {en} } @inproceedings{MuellerBurkovSchmeisser, author = {M{\"u}ller, Klaus and Burkov, Yevgen and Schmeißer, Dieter}, title = {Surface potential profiling on organic thin film transistors by photoemission-electron-microscopy (PEEM)}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {Surface potential imaging with Photoemission-electron-microskopy (PEEM) in high lateral resolution is introduced as a new tool for the characterisation of organic transistor structures. We use source-drain- electrode structures of different organic materials like carbon-black or graphite plotted on a printing foil. Semiconducting regioregular Poly(3-Hexylthiophene-2,5-diyl) (P3HT) was deposited by spin coating. For our measurements we used radiation of a standard high pressure Hg-lamp (4,9 eV) and synchrotron radiation at the BESSYII-U49/2 beam line. In contrast to Kelvin-AFM measurements of the surface potential, PEEM enables a simultaneous analysis of chemical composition by photoelectron spectroscopy. UPS, for example, at zero potential gives information on chemical homogeneity of the organic semiconductor in lateral resolution. PEEM images at applied voltages, compared with UPS-spectra, gives informations on doping profiles in the semiconductor, for example. In conclusion, PEEM should be a complementary method for characterisation of the surface potential with Kelvin-AFM. In addition, PEEM gives opportunities for measurements of chemical composition in the working state of the transistor (applied voltages).}, language = {en} } @inproceedings{MuellerPaloumpaHenkeletal., author = {M{\"u}ller, Klaus and Paloumpa, Ioanna and Henkel, Karsten and Schmeißer, Dieter}, title = {Organic Field Effect Transistors with polymer high-k dielectric insulator}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {Organic field effect transistors consisting of the copolymer poly(vinylidene fluoridetrifluoroethylene) (P(VDF-TrFE)) and P3HT (poly(3-hexlythiophene)) as active layer have been fabricated. The influence of P(VDF-TrFE) on the transconductance of organic field effect transistors was investigated and enhanced gate effects are observed compared to similar transistors with PMMA (Polymethylmetacrylate) as gate dielectric. Due to the high dielectric constant of P(VDF-TrFE) (DK=12) an operation voltage smaller than for a conventional organic dielectric like PMMA (DK=3.3) was observed. The thickness of the spincoated dielectric layers is in the range of 2microns and in consequence, no significant hysteresis was found, a prerequisite for transistor operation.}, language = {en} } @inproceedings{GeussMuellerPaloumpaetal., author = {Geuss, Markus and M{\"u}ller, Klaus and Paloumpa, Ioanna and Schmeißer, Dieter}, title = {Surface Potential profiling on operating full organic thin film transistors by Kelvin probe force microscopy}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {Kelvin-AFM is employed to study all polymer organic thin film transistors which are promising candidates for low cost - low performance applications like active matrix displays, sensors or single-serving devices. We use bottom contact source-drain- electrode structures of different organic materials like carbon-black or graphite plotted on a printing foil. Semiconducting regioregular Poly(3-Hexylthiophene-2,5-diyl) (P3HT) was subsequently deposited by spin coating. Surface potential profiles across the transistor channel were measured by Kelvin-AFM for various source-drain potential differences and signs. We found that contact resistances cause characteristic steps in the surface potential near the channel edges which vary with the electrode material. Furthermore, nonlinearities appear in the potential gradient which possibly give evidence for lateral inhomogeneities of the carrier mobilities. In summary, surface potential imaging with high lateral resolution ( approx. 100 nm) is introduced as a powerful tool for the characterisation of the transistor performance and the selection of suitable low cost electrode materials.}, language = {en} } @misc{BirkhoferDiehlAnderssonetal., author = {Birkhofer, Klaus and Diehl, Eva and Andersson, Jesper and Ekroos, Johan and Fr{\"u}h-M{\"u}ller, Andrea and Machnikowski, Franziska and Mader, Viktoria and Nilsson, Lovisa and Sasaki, Keiko and Rundl{\"o}f, Maj and Wolters, Volkmar and Smith, Henrik G.}, title = {Ecosystem services - current challenges and opportunities for ecological research}, series = {Frontiers in Ecology and Evolution}, volume = {2}, journal = {Frontiers in Ecology and Evolution}, issn = {2296-701X}, doi = {10.3389/fevo.2014.00087}, pages = {35}, language = {en} } @inproceedings{IsraelRachowSchwiertzetal., author = {Israel, Johannes and Rachow, Fabian and Schwiertz, Carola and Charlafti, Evgenia and M{\"u}ller, Klaus and Schmeißer, Dieter}, title = {Direct CO2-Methanation of flue gas emitted by conventional power plants}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, pages = {S. 255}, abstract = {The catalytic conversion of CO2 with H2 into CH4 is possible by the Sabatier reaction CO2+4H2→CH4+2H2O. Using excess energy from renewable electricity generation, this approach offers an opportunity for recycling of CO2 as synthetic natural gas. In a new concept, we investigate the performance of the Sabatier reaction as direct methanation of flue gas, emitted by conventional power plants. We investigate the Sabatier process in an upscaled system, with a maximum input flow rate of 45 Nm3/h Gas. The performance is investigated in a simulated composition of flue gas and under real conditions at a lignite power plant in Schwarze Pumpe, Brandenburg, Germany. We can achieve a CO2-conversion of up to 90\%, with approx. 100\% selectivity towards CH4. Under flue gas conditions and at a certain limit of gas flow the system is operated at an autothermal running modus, a steady state equilibrium of exothermic heat production and thermal flow that needs neither external annealing nor cooling.}, language = {en} } @inproceedings{RachowHagendorfMuelleretal., author = {Rachow, Fabian and Hagendorf, Moritz and M{\"u}ller, Klaus and Schmeißer, Dieter}, title = {Synthesis of Methanol from CO2 for Power-to-Liquid applications}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, pages = {S. 256}, abstract = {The direct synthesis of methanol [CO2+3H2->CH3OH+H2O] represent a possibility to reduce the global CO2-emission by recycling the CO2 and also to store excess energy from renewable energy sources into a common fuel or chemical feedstock (Power-to-Liquid). For an acceptable conversion rate of CO2 a catalyst is needed, together with high temperatures (>200°C) and high pressure (50-200bar). Methanol is normally produced form synthesis gas, a mixture of CO and H2. By directly using CO2 for the exothermic reaction, we avoid the conversion of CO2 to CO by the reversed water gas shift reaction. We also present new concepts for the conversion from CO2-rich flue gases, eliminating the need for a separation of the CO2. The concept is backed up by measurements in laboratory scale. Here we use a Cu-ZnO catalyst on a ZrO2 substrate prepared by impregnation and compare the results with commercially available catalysts. We achieved a conversion of around 7\% and a selectivity of 60\% at a temperature of 240°C and 45bar. The reaction is thermodynamically limited with a maximum conversion rate of 15\% at 250°C and 50bar. The conversion and the selectivity towards methanol is highly influenced by the catalyst used, the temperature, the pressure as well as the flow rate of the reactants.}, language = {en} } @misc{MuellerBaerHenkeletal., author = {M{\"u}ller, Klaus and B{\"a}r, Werner and Henkel, Karsten and Jahnke, Agnes and Schwiertz, Carola and Schmeißer, Dieter}, title = {Organische Feldeffekttransistoren als Transducer in der Biosensorik}, series = {Technisches Messen}, volume = {70}, journal = {Technisches Messen}, number = {12}, issn = {0171-8096}, doi = {10.1524/teme.70.12.565.20261}, pages = {565 -- 568}, abstract = {In diesem Beitrag wird der Einsatz neuartiger Sensortypen f{\"u}r die medizinische Diagnostik beschrieben. Diese Sensoren sollen komplett organisch sein und auf dem Prinzip des Feldeffekttransistors basieren. Als Modellsystem f{\"u}r die Anwendung in der Biosensorik soll die Einsatzm{\"o}glichkeit dieser Sensoren in der nicht-invasiven Diagnostik der Helicobacter-pylori-Infektion {\"u}berpr{\"u}ft werden.}, language = {de} } @misc{MuellerRachowIsraeletal., author = {M{\"u}ller, Klaus and Rachow, Fabian and Israel, Johannes and Charlafti, Evgenia and Schwiertz, Carola and Schmeißer, Dieter}, title = {Direct Methanation of Flue Gas at a Lignite Power Plant}, series = {International Journal of Environmental Science}, journal = {International Journal of Environmental Science}, number = {2}, issn = {2367-8941}, pages = {425 -- 437}, abstract = {The combustion of fossil fuels results in CO2 emission, which is one of the primary causes of global warming. An important approach for solving this problem is the fixation, the chemical utilization and the recycling of CO2. Therefore, we investigate the catalytic conversion of CO2 with H2 into methane (CH4) with an upscaled test station at a brown coal power plant. In a completely new strategy, we realize the direct conversion of the CO2 content of the flue gas, without a cleaning process like amine scrubbing or optimized combustion like oxyfuel. Our experiments are performed in matters of catalytic performance, heat production and stability of the catalytic Sabatier process, as a function of the gas flow rate. The catalytic performance is investigated with a simulated composition of flue gas and under real conditions directly at the power plant. The CH4 production by the Sabatier process is realized with a maximum input flow rate of near 50Nm3/h, with 30Nm3/h flue gas and 20Nm3/h hydrogen. For these values, the necessary power scale for hydrogen generation by electrolysis is around 100kW. With synthetic and real flue gas, a conversion up to 99\% (for hydrogen surplus) with 100\% selectivity is stabilized. The reaction operates in thermal steady state equilibrium without any external energy supply. In consequence, the process of CO2 recycling could be integrated directly as a post combustion process of conventional power plants, without an expensive capturing step, for example.}, language = {en} } @incollection{HenkelHaeberleMuelleretal., author = {Henkel, Karsten and Haeberle, J{\"o}rg and M{\"u}ller, Klaus and Janowitz, Christoph and Schmeißer, Dieter}, title = {Preparation, properties and electronic structure of SnO₂}, series = {Single Crystals of Electronic Materials}, booktitle = {Single Crystals of Electronic Materials}, editor = {Fornari, Robert}, publisher = {Elsevier, Woodhead Publishing}, address = {Duxford}, isbn = {978-0-08-102096-8}, pages = {547 -- 572}, abstract = {This chapter reports about tin oxide (SnO₂), a material which belongs to the transparent conducting oxide family and is best characterized by its high conductivity, high carrier mobility, and the ability to form p-type conductivity. We correlate these properties in terms of localized intrinsic electronic defect states which are resolved by resonant photoelectron spectroscopy measurements. We describe SnO₂ in terms of an inhomogeneous, mixed-ionic-covalent semiconductor in which these intrinsic electronic defects state are stabilized.}, language = {en} }