@inproceedings{MuellerMandalHenkeletal., author = {M{\"u}ller, Klaus and Mandal, Dipankar and Henkel, Karsten and Paloumpa, Ioanna and Schmeißer, Dieter}, title = {Interface reactions of ferroelectric copolymer layers with different electrode materials}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 43}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 43}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 830}, abstract = {The ferroelectric copolymer poly(vinylidene fluoride trifluoroethylene) (P(VDF-TrFE)) is a possible material for low cost applications as organic nonvolatile memory element. We present an XPS interface investigation of the copolymer/electrode interface. Below 100nm film thickness, interface phenomena becomes important. Possible interface reactions could lead to a reduction of the ferroelectric functionality.We present a comparative study of the two interfaces Al/P(VDF-TrFE) and PEDOT:PSS/P(VDF-TrFE). The result is a clear indication of a surface reaction in between the Aluminum-electrodes. In contrast, for PEDOT:PSS the measurements shows a layer by layer formation of the interface PEDOT:PSS/PVDF without any reaction. Second, we present a study of remanent polarization of ultrathin spincoated films of the copolymer, in a thickness range from 5 to 100mn, with organic electrodes like PEDOT:PSS. The measurements are carried out by using the flatband shift of a capacitance-voltage (CV) characteristic. This shift of flatband voltage is used as value for the electric polarization of the polymer.}, language = {en} } @inproceedings{HenkelTorcheSchwiertzetal., author = {Henkel, Karsten and Torche, Mohamed and Schwiertz, Carola and Paloumpa, Ioanna and Sohal, Rakesh and M{\"u}ller, Klaus and Schmeißer, Dieter}, title = {Inorganic and organic layers for high-k and organic memory applications}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 41}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 41}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 127}, abstract = {We report about organic and inorganic MIS stacks for new possibilities for high frequency and high power applications as well as for non volatile memory cell. The organic stack contains a ferroelectric polymer as the functional layer. Poly[vinylidene fluoride trifluoroethylene] (P[VDF/TrFE]) is spin coated from a solution onto oxidised silicon substrates. We report on the polarisation induced flatband voltage shifts. For the inorganic stack our attempt is to combine higk-k dielectrics with high band gap semiconductors (SiC). Praseodymium oxide layers are prepared by electron beam evaporation from Pr6O11 powder and in situ controlling of interface and volume composition (XPS). Praseodymium silicate layers were prepared either by metal evaporation onto a thin ox- ide on top of the semiconductor and following annealing steps or by a wet chemical process out of aqueous Pr(NO3)3 solutions. Using spectro-scopic characterisation we investigate the stability of the various inter-faces within the stacks as well as the reactivity of the metal electrodes on thin Pr2O3. We report the results of electrical characterisation consisting of permittivity values, leakage current and density of interface states.}, language = {en} } @inproceedings{MuellerHenkelPaloumpaetal., author = {M{\"u}ller, Klaus and Henkel, Karsten and Paloumpa, Ioanna and Schmeißer, Dieter}, title = {P(VDF/TrFE) as ferroelectric insulation layer for organic field effect transistors}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 41}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 41}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 101}, abstract = {The ferroelectric polymer poly(vinylidene fluoride trifluoroethylene)(P(VDF-TrFE)) is used as insulating material for organic field effect tran-sistors (OFET) and metal-insulator-semiconductor (MIS)-structures. For the MIS-structures, we find the typical hysteresis in the CV charac-teristic upon increasing the voltage scan window. Based on these results, we fabricate OFET with regioregular poly(3-hexlythiophene)(P3HT) as organic semiconductor. The transistors are constructed in bottom gate architecture with thin layers of spincoated P(VDF-TrFE) as gate insulation (100nm). The drain-source current of the OFET is reversible affected by the polarized gate, which gives opportunities for organic nonvolatile memory elements. We present characteristic features like the hysteretic drain current response or the data retention. Furthermore, we present measurements with Kelvin probe force microscopy, a method which gives informations on the lateral distributions of the surface potential.}, language = {en} } @inproceedings{RichterMuellerPhilipetal., author = {Richter, Matthias and M{\"u}ller, Klaus and Philip, Shine and Paloumpa, Ioanna and Henkel, Karsten and Schmeißer, Dieter}, title = {Temperature dependence of organic solar cell parameters}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 44}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 44}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 671}, abstract = {The influence of an annealing step on the parameters of bulk heterojunction organic solar cells is investigated. In order to fabricate the solar cells we use glass coated with ITO (Indiumtinoxide) as a substrate on which the active layer consisting of P3HT and PCBM is spincoated. Al-electrodes are evaporated on top of the active layer. We use PEDOT:PSS as buffer layer. Each sample is annealed at different temperatures for a short time. Between every temperature step the I-V characteristic of the cell is measured. The following parameters are derived afterwards: FF, Isc (density), Voc. Also the efficiency is estimated. The results show a maximum cell efficiency for drying at 100°C for 20sec. A further important step for preparation is the drying procedure of the PEDOT:PSS layer. Here an improvement of about 50\% in cell efficiency is measured after drying at 50°C for 5 days under inert gas atmosphere.}, language = {en} } @inproceedings{MbuaMuellerRichteretal., author = {Mbua, Roy and M{\"u}ller, Klaus and Richter, Matthias and Henkel, Karsten and Paloumpa, Ioanna and Schmeißer, Dieter and Kramm, Ulricke}, title = {Investigation of new Catalysts for PEM Fuel Cells}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 483}, abstract = {Increasing green house emissions amplify global warming concerns worldwide. Fuel cells, based on polymer electrolyte membranes (PEM) are part of the solution to this issue. We aim at developing and testing new catalysts for fuel cells. Platinum catalysts perform best in PEM fuel cells to date but they are very expensive. For fuel cells to be perfectly applicable and economically affordable, an alternative catalyst with similar or even greater efficiency should be developed. Metal phthalocyanines are known to be good oxygen reduction catalysts and are associated with high electron transfer properties. We investigated Cobalt Phthalocyanine in its pure state mixed with Carbon Black (CoPc:Carbon Black=1:9) untreated and also after a treatment in N2 at several temperatures, up to 1000°C for 30 minutes. Results of XPS and EDX analyses reveal that the treatment at higher temperatures causes a rearrangement in the chemical states of Co, N and C atoms. Furthermore, results of cycling voltammetry (CV) analysis reveal that CoPc treated in N2 at 800°C exhibited a higher current density, in conclusion, a higher catalytic activity than the untreated CoPc.}, language = {en} } @inproceedings{PhilipMartinezMuelleretal., author = {Philip, Shine and Martinez, Elias and M{\"u}ller, Klaus and Kunst, Marinus and Schmeißer, Dieter}, title = {Time resolved microwave conductivity measurements of Bulk Heterojunction solar cells}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 301}, abstract = {The time resolved microwave conductivity (TRMC) method was used in order to study the generation and decay kinetics of charge carriers in the Bulk Heterojunction (BHJ) solar cells. The charge carriers were generated with 532nm laser pulses of 10ns FWHM (Full Width at Half Maximum) induced in the cells. The BHJ solar cells used for the measurements had a photoactive layer consisting of a mixture of Poly (3-Hexylthiophene) P3HT and Phenyl-C61-butyric acid methyl ester (PCBM) which was spin coated onto Indium tin oxide (ITO)/glass substrates. In the field of Organic photovoltaic blends, TRMC method is introduced as a new method of direct investigation of the charge carrier lifetime as well as the charge carrier mobility and we were successful in studying the charge carrier lifetime of the reference BHJ solar cells. We also studied the influence of aligned ferroelectric fields on the charge separation in BHJ solar cells. As ferroelectric material, we used the copolymer Poly (vinylidene fluoride - trifluoroethylene) P(VDF-TrFE).}, language = {en} } @inproceedings{MuellerHoffmannbeckKirneretal., author = {M{\"u}ller, Klaus and Hoffmannbeck, David and Kirner, Georg and St{\"a}dter, Matthias and Schmeißer, Dieter}, title = {CO2-Methanation by Catalytic Conversion}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {The utilization of CO2 as raw material is an important component of a program for CO2 reduction. A possibility is the production of methane. At a moderate temperature of around 350°C, hydrogenation of CO2 to methane is possible by the Sabatier reaction CO2 + 4H2 ->CH4 +2H2O. Prerequisite for an efficient kinetics of the Sabatier reaction is the application and optimization of catalysts. In this contribution, we present investigations of Ru and Ni catalysts on different substrates. For Ru/Al2O3 catalysts, we found stable operation without degradation within 500 hours with a conversion rate of 80\% at 350°C. For NiO/SiO2 catalysts, a conversion rate of 90\% was found for temperatures of 350-405°C. We also show the investigation of cross sensitivities against SOx and NOx, which are typical contaminations of CO2, generated by the industrial oxyfuel process. In our work the morphology (REM, AFM, specific surface), chemical composition (FTIR, XPS) and phase composition (XRD) of the catalysts are characterized. In addition, we report on thermodesorption (TDS) measurements at atmospheric pressure to determine the amount of adsorbed CO2 under real conditions. The project is funded by the German Ministry of Research and Education (BMBF-GeoEn).}, language = {en} } @inproceedings{PhilipMuellerRichteretal., author = {Philip, Shine and M{\"u}ller, Klaus and Richter, Matthias and Kunst, Marinus and Schmeißer, Dieter}, title = {Study of excited states and a model for exciton-polaron interaction in P3HT}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 47}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 47}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {Organic semiconductors efficiently harvest light in the region of the solar spectrum due to a high absorption/extinction coefficient.In our work we study the electronic structure and the charge carrier dynamics of polymeric organic semiconductor regioregular poly(3-hexylthiophen-2,5-diyl) (P3HT), an ideal p-type semiconductor and a widely used conjugated polymer, and blends with the fullerene derivative phenyl-C61-butyric acid methyl ester (PCBM), an electron acceptor material. The study was done with the help of time resolved microwave conductivity (TRMC) for contactless investigation of bulk carrier dynamics, optical spectroscopy, ultraviolet photoelectron spectroscopy(UPS) and high resolution X-ray absorption spectroscopy(XAS) which investigates excited states of rr-P3HT. From the data obtained we could infer the positions of the valence and conduction band, the existence of two excitons as well as the co-existence of one dimensional and two dimensional polarons. Based on our spectroscopic data we propose a model in which the scattering of virtual polarons and excitons are shown to create mobile polaronic charge carriers.}, 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 = {Self restriction oft the Sabatier reaction in large scale}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {A main goal for a sustainable energy supply is a long term energy storage system. One opportunity in this research field is the power to gas concept, where the produced gas can be fed in the existing network of natural gas. Here we show in a technical scale how the direct CO2 conversion to methane according the Sabatier reaction, CO2 + 4 H2 → CH4 + 2H2O , is self organized. At a certain limit of gas flow, a steady state equilibrium of exothermic heat production and thermal flow is reached and the reaction needs no further external annealing. We find for the maximum volume rate at the steady state equilibirum a shift of around 250 ∘C above the optimized temperature of the catalytic supported chemical equilibrium. It is shown that also with this setup the used catalyst works with a stable conversion higher than 80 \% under the reached temperature and given pressure conditions.}, language = {en} } @inproceedings{RachowIsraelSchwiertzetal., author = {Rachow, Fabian and Israel, Johannes and Schwiertz, Carola and Charlafti, Evgenia and M{\"u}ller, Klaus and Schmeißer, Dieter}, title = {CO2 Methanation with different gas mixtures}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 539}, abstract = {A key issue in the Energiewende in Germany is the storage of excess energy, as it enables energy management systems to react to fluctuating sources and enhances the flexibility of an energy mix. Power to Gas may be the most reasonable approach to store the energy in the form of hydrogen or synthetic natural gas. We study the direct conversion of CO2 by the Sabatier reaction to gain a methane based mixture which can replace natural gas in CHP plants and gas motors and can help to partially reduce the CO2 emission. In laboratory scale we investigated the performance (with IR and QMS) of Ni-based catalyst for different sources of CO2 like clean CO2, CO2 emitted as flue gas from an Oxyfuel power plant or a synthetic mixture with O2, N2 and SO2 in concentration typical for conventional power plants. Measurements from an up-scaled system are also presented, showing data important for a technical application. Here, we are able to convert more than 200kg CO2/day with conversion rates up to 90\%.}, language = {en} } @incollection{Mueller, author = {M{\"u}ller, Klaus}, title = {Untersuchungen auf der Akropolis von Assos}, series = {Assos - Neue Forschungsergebnisse zur Baugeschichte und Arch{\"a}ologie der s{\"u}dlichen Troas}, booktitle = {Assos - Neue Forschungsergebnisse zur Baugeschichte und Arch{\"a}ologie der s{\"u}dlichen Troas}, editor = {Arslan, Nurettin and Mohr, Eva-Maria and Rheidt, Klaus}, publisher = {Habelt}, address = {Bonn}, isbn = {978-3-7749-3951-6}, pages = {53 -- 83}, language = {de} } @inproceedings{MuellerSchmeisser, author = {M{\"u}ller, Klaus and Schmeißer, Dieter}, title = {Carbon-plot-microstructuring for all-polymer-transistors}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {This contribution describes the use of a low-cost technology to form organic microstructures for electronical applications. We demonstrate the principle ability of this method through the fabrication of organic field effect- transistors. With a computer driven plotter, substrates like printing foil and colloidal graphite (diluted in water) for the electrodes, we realized channel lengths of 20+10 micrometers. Compared with transistor devices, fabricated using conventional photolithographic methods and the same semiconducting material, this technique is a hopefull approach to produce microelectronic structures that are low-cost and all-organic.}, language = {en} } @inproceedings{MuellerMilkoBurkovetal., author = {M{\"u}ller, Klaus and Milko, Sergey and Burkov, Yevgen and Schmeißer, Dieter}, title = {Mischkristalle des Systems ZnS-CuInS2 f{\"u}r multispektrale Solarzellen}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {Wir haben CuInS2 (CIS) unterschiedlicher Herstellung (Koverdampfung, Sputtern, Pulsed Laser Deposition, CIS auf Kupferband aufgebracht) untersucht. Neben Tiefenprofilen (durch Sputtern) der Elementverteilung dieser Proben wurden der Einfluss der Temperatur, von aufgedampftem Kupfer und Indium, ebenfalls bei verschiedenen Temperaturen, auf das Verhalten der St{\"o}chiometrie mit spektroskopischen Methoden (XPS, UPS) studiert. Parallel dazu wurde das Verhalten von im Vakuum aufgedampften ZnS und die entsprechenden Oberfl{\"a}chenreaktionen in Abh{\"a}ngigkeit von der Temperatur untersucht und charakterisiert, so dass Aussagen {\"u}ber die Optimierung und Anpassung von Pr{\"a}parationsbedingungen und Parametern zur Herstellung von erstens reinem CIS und zweitens von Mischkristallen des Typs Zn2-xCuxInxS2 m{\"o}glich werden. Zwischen den beiden Endgliedern ZnS und CuInS2 besteht bis auf einen Phasen{\"u}bergang bei etwa 80\% CIS l{\"u}ckenlose Mischbarkeit gem{\"a}ss Zn2-xCuxInxS2 (Bente: Chem.Erde (1991)). Die elektronische Bandl{\"u}cke dieser Mischkristalle l{\"a}sst sich im Vergleich zu reinem CuInS2 in einem Bereich von 3,67 eV (ZnS) bis 1,55 eV (CuInS2) variieren. Damit besteht die M{\"o}glichkeit, durch kontrollierte {\"A}nderung der Zusammensetzung der Schichten die Effizienz von Solarzellen aus diesem Material zu optimieren.}, language = {de} } @inproceedings{FleigeMuellerSchmeisser, author = {Fleige, Michael and M{\"u}ller, Klaus and Schmeißer, Dieter}, title = {Sabatier based CO2-Methanation of flue gas in conventional power plants}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {Already discovered by Paul Sabatier in 1902 the Hydrogenation according to CO2 + 4H2 ->CH4 + 2H2O nowadays is discussed in the course of the 'Power-to-Gas' approach to utilize excess energy from renewable electricity generation in times of oversupply of electricity. We investigate the behavior of this process in a simulated flue gas atmosphere of conventional base load power plants, which could be used as constant sources of the reactant CO2. Therefore the influence of different flue gas compositions such as varying contents of nitrogen and residual oxygen are tested in a laboratory scale. The heterogeneous catalysis process is investigated with regard to conversion rates, yield and selectivity and long-term stability of the Ni-catalyst. Earlier results of stable operating conditions in a 1:1 mixture of nitrogen and reactants, which is a typical ratio for flue gas in conventional power plants, could be confirmed in a first step.}, language = {en} } @inproceedings{IsraelMuellerRachowetal., author = {Israel, Johannes and M{\"u}ller, Klaus and Rachow, Fabian and Beuckert, Guido and Schmeißer, Dieter}, title = {Reaction kinetics of the Sabatier Reaction in a demonstration plant}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {We currently build up a demonstration plant for the direct catalytic conversion of CO2 into methane according to the Sabatier reaction CO2+4H2→CH4+2H2O. We have already reached conversion rates higher than 90\% and a selectivity close to unity in our laboratory experiments with NiO based catalysts. A good long term stability was obtained with a reactant gas flow density of 0.8 l/min cm2· at 350∘C. We will study the process now on a larger scale with a factor 10000. The process is controlled via mass flow controllers with a throughput of 20m3/h H2 and 5m3/h CO2 at an inlet gas pressure of up to 15 bar, the temperature is regulated by a PID multichannel controller. As water is a by-product we use an efficient cooling trap for its separation form the obtained methane. The reaction products are analyzed by a quadrupole mass spectrometer under reaction conditions. We start our experiments in using clean CO2 and H2. Later experiments will involve industrial quality (oxy-fuel) conditions also. Goal of this project is to determine the performance of the catalytic process under conditions which enable an industrial implementation in energy storage concepts. In this contribution we report of the design of a demonstration plant and on first experiments concerning the kinetics within the system.}, language = {en} } @inproceedings{RachowMuellerSchmeisser, author = {Rachow, Fabian and M{\"u}ller, Klaus and Schmeißer, Dieter}, title = {Sabatier based Methanation of carbon dioxide and Catalyst stability against contaminations}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {The Sabatier-Reaction [CO2+4H2→CH4+2H2O] represents a possible way for the reduction and utilization of CO2 produced in the oxy-fuel combustion process. While using different ruthenium and nickel based catalysts we studied the catalytic performance with quadrupole mass spectroscopy and IR-spectroscopy in terms of conversion of CO2,yield of CH4, selectivity and stability. Conversions of up to 90\% and a selectivity of well above 95\% could be achieved. Further studies focus on the long term stability, especially with the influence of contaminations like SOx and NOx as they may occur in oxy-fuel or flue gas and could greatly reduce the life time of a catalyst. We investigate the limits of Ni based catalysts for those additives. However, technical oxy-fuel gas seems to have no particular effect on the activity of a commonly used NiO-catalyst when compared to quasi pure CO2 , showing only a small drop of performance after five days with a constant conversion rate of over 80\% at the end.}, language = {en} } @inproceedings{GoriachkoMuellerPaloumpaetal., author = {Goriachko, Andrii and M{\"u}ller, Klaus and Paloumpa, Ioanna and Schmeißer, Dieter}, title = {Scanning Kelvin Probe Microscopy Investigations of Au-P3HT-Au structures for Organic Field Effect Transistors}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {We report on the scanning Kelvin probe microscopy (SKPM) investigation of the source-channel-drain structures of organic field effect transistor (OFET). A poly-3-hexyl-thiophen (P3HT) organic semiconductor film, spin-coated on a glass-substrate and 65 nm thick, is used as a 2 mkm channel between Au source (drain) electrodes. Depending on the preparation conditions, the P3HT film consists of either amorphous nm-seized molecular clsuters or mkm-long chains. The SKPM allows mapping of electric potential along with the surface topography on the DC-biased structures (8V applied between source and drain). It reveals a linear potential fall in the channel region as well as the abscence of potential jumps (contact resistance) in the electrode/channel regions. This is a direct indication of the top-gate OFET type advantage, which the given structure is suited for. Due to the high spatial resolution of the UHV-based SKPM, doping inhomogenities of the p-type P3HT semiconductor as well as the space charge region on the electron injecting electrode are observed. In addition we present SKPM investigations of the structure with source and drain electrodes but without a semiconductor, showing electric field configuration for the given electrodes geometry.}, language = {en} } @inproceedings{SohalHenkelMuelleretal., author = {Sohal, Rakesh and Henkel, Karsten and M{\"u}ller, Klaus and Schmeißer, Dieter}, title = {Growth and Characterization of 3C-SiC thin films on Si substrates}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {This work reports on the growth and characterization of cubic silicon carbide thin films. A cold wall low pressure chemical vapour deposition (LPCVD) system has been used to grow the cubic silicon carbide. The two step method, carbonization and subsequent growth, has been used to grow good quality 3C-SiC thin films. The composition and structure of deposited thin films have been analysed by Fourier Transform Infrared Spectroscopy (FTIR), XPS and X-Ray Diffractometry (XRD). The structural quality of the films has been optimized as a function of substrate temperature during carbonization and growth. X-rays diffraction measurements shows that the grown layers are highly oriented crystalline cubic silicon carbide.}, language = {en} } @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} }