TY - GEN A1 - Kot, Małgorzata A1 - Das, Chittaranjan A1 - Wang, Zhiping A1 - Henkel, Karsten A1 - Rouissi, Zied A1 - Wojciechowski, Konrad A1 - Snaith, Henry J. A1 - Schmeißer, Dieter T1 - Room-Temperature Atomic Layer Deposition of Al₂O₃: Impact on Efficiency, Stability and Surface Properties in Perovskite Solar Cells T2 - ChemSusChem N2 - In this work, solar cells with a freshly made CH₃NH₃PbI₃ perovskite film showed a power conversion efficiency (PCE) of 15.4 % whereas the one with 50 days aged perovskite film only 6.1 %. However, when the aged perovskite was covered with a layer of Al₂O₃ deposited by atomic layer deposition (ALD) at room temperature (RT), the PCE value was clearly enhanced. X-ray photoelectron spectroscopy study showed that the ALD precursors are chemically active only at the perovskite surface and passivate it. Moreover, the RT-ALD-Al2O3-covered perovskite films showed enhanced ambient air stability. KW - Al₂O₃ KW - atomic layer deposition (ALD) KW - perovskite KW - solar cells KW - X-ray photoelectron spectroscopy (XPS) Y1 - 2016 U6 - https://doi.org/10.1002/cssc.201601186 SN - 1864-5631 SN - 1864-564X VL - 9 IS - 24 SP - 3401 EP - 3406 ER - TY - GEN A1 - Cuypers, Daniel A1 - Fleischmann, Claudia A1 - Dorp, Dennis H. von A1 - Brizzi, Simone A1 - Tallarida, Massimo A1 - Müller, Matthias A1 - Hönicke, Philipp A1 - Billen, Arne A1 - Chintala, Ravi A1 - Conard, Thierry A1 - Schmeißer, Dieter A1 - Vandervorst, Wilfried A1 - Elshocht, Sven van A1 - Armini, Silvia A1 - De Gendt, Stefan A1 - Adelmann, Christoph T1 - Sacrificial Self-Assembled Monolayers for the Passivation of GaAs(100) Surfaces and Interfaces T2 - Chemistry of Materials N2 - The use of sacrificial self-assembled monolayers (SAMs) to prepare clean n-type GaAs (100) surfaces without band bending in vacuo is demonstrated. GaAs surface passivation using octadecanethiol SAMs after HCl cleaning is shown to lead to an enhancement of the room-temperature photoluminescence intensity. Synchrotron-radiation photoelectron spectroscopy (SRPES) finds that the interfacial oxide between GaAs and the SAM remains below the detection limit. Evidence for both Ga–S and As–S bonds at the GaAs–thiolate interface is found. The limited thermal stability of the SAM allows the desorption of the alkyl chains by in situ thermal annealing at temperatures above 180 °C, leaving S bonded to Ga behind. The resulting surface contains only a very small amount of O (0.05 ML coverage) and C (about 3% of the SAM remaining) and shows no band bending with the surface Fermi level close to the conduction band. Atomic layer deposition of Al₂O₃ on this surface occurs via the formation of Al–S bonds without introducing any additional band bending. This indicates that the surface preparation of n-type GaAs (100) using sacrificial octadecanethiol SAMs followed by in situ thermal removal provides a route toward GaAs/oxide interfaces without interfacial oxides and without band bending. KW - GaAs KW - passivation KW - Al₂O₃ KW - atomic layer deposition (ALD) KW - Synchrotron-radiation photoelectron spectroscopy (SRPES) KW - self assembled monolayers (SAM) KW - interface engineering Y1 - 2016 U6 - https://doi.org/10.1021/acs.chemmater.6b01732 SN - 0897-4756 SN - 1520-5002 VL - 28 IS - 16 SP - 5689 EP - 5701 ER - TY - GEN A1 - Corrêa, Silma Alberton A1 - Brizzi, Simone A1 - Schmeißer, Dieter T1 - Depicting the Electronic Structure of HfO₂ Films by Spectroscopic Techniques T2 - ECS Transactions N2 - The electronic structure of HfO₂ films was investigated. The partial density of states for the valence and the conduction bands was determined by the detailed analysis of the O1s resonance profile by resonant photoelectron spectroscopy. The positions of valence band maximum and conduction band minimum, the excitation range for the polaronic states and the range of charge transfer band were found to be not influenced by the preparation conditions. The band gap was determined to be 6.2 eV and the energy of the charge neutrality level (referred to vacuum level) was determined as 4.7 eV. The Fermi level position was observed to vary about 1.2 eV depending on the preparation conditions, which indicates the presence of charges within the films. KW - HfO₂ KW - resonant photoelectron spectroscopy (resPES) KW - electronic structure KW - partial density of states KW - charge neutrality level Y1 - 2016 U6 - https://doi.org/10.1149/07506.0145ecst SN - 1938-6737 SN - 1938-5862 VL - 75 IS - 6 SP - 145 EP - 153 ER - TY - GEN A1 - Henkel, Karsten A1 - Das, Chittaranjan A1 - Kot, Małgorzata A1 - Schmeißer, Dieter A1 - Naumann, Franziska A1 - Kärkkänen, Irina A1 - Gargouri, Hassan T1 - In-gap states in titanium dioxide and oxynitride atomic layer deposited films T2 - Journal of Vacuum Science and Technology: A N2 - Valence band (VB) spectra of titanium dioxide (TiO2) and oxynitride (TiOxNy) films prepared by different atomic layer deposition (ALD) processes are compared and related to electrical characterization [current–voltage (JV) and capacitance–voltage (CV)] results. By increasing the nitrogen amount in the TiO2 film, band-gap narrowing is observed. The band-gap decrease is related to the contribution of the nitrogen density of states, which induces defects within the band-gap and thus reduces its optical band-gap. In-gap states are found in the VB spectra at 1 eV below the Fermi energy in all investigated ALD samples, i.e., in TiO2 as well as in TiOxNy films. An exponential correlation between leakage current density and in-gap state intensity is derived by the combination of JV measurements and VB spectra, whereas the in-gap states seem to have no influence on hysteresis and fixed oxide charges found in the CV data. It is argued that the in-gap states in TiO2 and TiOxNy have an excitonic or polaronic origin. Both, band-gap narrowing and in-gap state intensity can be tuned by the ALD process selection and the variation of its parameters. KW - Titanium dioxide (TiO2) KW - Titanium oxynitrdie (TiON) KW - valence band spectra KW - in-gap states KW - band-gap narrowing KW - electrical characterization Y1 - 2017 U6 - https://doi.org/10.1116/1.4972247 SN - 0734-2101 SN - 1520-8559 VL - 35 IS - 1 SP - 01B135-1 EP - 01B135-8 ER - TY - CHAP A1 - Garain, Samiran A1 - Adhikary, Prakriti A1 - Mandal, Dipankar A1 - Sen, Shrabanee A1 - Henkel, Karsten A1 - Schmeißer, Dieter T1 - Electro-active β-Phase Formation in Poly(vinylidene fluoride) Films by Hydrated Rare earth Metal Salt T2 - Proceeding of the International Conference on Nanotechnology 2013 (ICNT 2013) N2 - Polyvinylidene fluoride (PVDF) is a typical fluoro-polymer with complicated polymorphisms due to the semi-crystalline nature. Generally, four crystalline phases, α, β, γ and δ may exist in PVDF crystals. The nonpolar α- and δ-phase has a monoclinic lattice with trans-gauche conformation (TGTG⁄), which is thermodynamically most stable for PVDF. The polar β phase with all-trans (TTTT) planar zigzag conformation is attractive for its piezo-, pyro-, and ferroelectric properties. The polar β-Phase and also semi-polar γ-phase (TTTGTTTG⁄) have obtained wide device applications such as acoustic transducers, piezoelectric sensors, energy harvesting generators, pyroelectric sensors, non-volatile memories and energy storage capacitors. In this work, we explore the possibility to nucleate β-phase in PVDF hydrated salt composite films by addition of the hydrated Rare earth metal salt, (NH4)4 Ce (SO4)4, 2H2O) for the piezo- ferro and high dielectric based device applications. It has been found that the water molecules in (NH4)4 Ce (SO4)4, 2H2O could form hydrogen bonds with PVDF during the crystallization process and the hydrogen bonds promoted the electro-active crystalline β- phase in PVDF with all -trans conformations. In addition, the DMF (solvent used for films preparation) can also assist the rare-earth based nanoparticle preparation, as a result the electrostatic interaction of the surface charge of the nanoparticles and molecular dipoles in PVDF can resist the electroactive β- phase in PVDF. KW - PVDF KW - β-Phase KW - piezoelectric Y1 - 2013 SN - 978-81-927756-0-9 SP - S. 127 PB - Institute of Technology, Haldia, WB, India CY - Haldia ER - TY - CHAP A1 - Schmeißer, Dieter A1 - Müller, Sebastian A1 - Henkel, Karsten A1 - Müller, Klaus A1 - Wehner, Stefan T1 - In-situ analysis of moving reaction fronts for the bistable CO oxidation reaction on noble metal catalyst T2 - Extended Abstracts Book of First International Conference on Materials for Energy N2 - Experimental data on the reaction kinetics of catalytic processes are prerequisite for modeling of such reactions and their output. We investigate the CO oxidation on some noble metal catalysts, like Iridium(111) and Palladium(111) which is a bistable surface reaction. In a specific range of CO content in the feed gas islands of one or the other adsorbate nucleate and grow, which is recorded with photo electron emission microscopy (PEEM). During these transients the coverage on the surface changes from predominantly oxygen covered to predominantly CO covered resp. vice versa. But the resolution of PEEM and especially its unknown and nonlinear dependence of coverage of the two adsorbates (oxygen and CO) and image intensity make it impossible to extract the changes in coverage. On the other hand the reaction diffusion model based on the Langmuir-Hinshelwood-mechanism delivers the coverage of oxygen and carbon monoxide. The shapeand wall velocity of those islands has been connected perfectly to each other [CPL 423 (2006) 39], but not the absolute coverage and their variation during the reaction. Since the domain wall velocity is small on Iridium(111), this has opened the possibility for a detailed analysis of the changing coverage inside this domain wallutilizing synchrotron radiation and photo electron spectroscopy at BESSY II. The coverage profile of oxygen and CO inside a moving domain wall was measured for both cases using XPS spectra at O1s, C1s and the valence band during thereaction. Comparison with the reaction-diffusion-model and other catalytic surfaces, like Palladium(111) are done. KW - CO oxidation KW - Ir KW - Pd KW - photo electron emission microscopy (PEEM) Y1 - 2010 SN - 978-3-89746-117-8 SP - S. 932 PB - Dechema e.V. CY - Frankfurt ER - TY - GEN A1 - Menezes, Prashanth W. A1 - Indra, Arindam A1 - Das, Chittaranjan A1 - Walter, Carsten A1 - Göbel, Caren A1 - Gutkin, Vitaly A1 - Schmeißer, Dieter A1 - Driess, Matthias T1 - Uncovering the Nature of Active Species of Nickel Phosphide Catalysts in High-Performance Electrochemical Overall Water Splitting T2 - ACS Catalysis N2 - A systematic structural elucidation of the near-surface active species of the two remarkably active nickel phosphides Ni12P5 and Ni2P on the basis of extensive analytical, microscopic, and spectroscopic investigations is reported. The latter can serve as complementary efficient electrocatalysts in the hydrogen (HER) versus oxygen evolution reaction (OER) in alkaline media. In the OER Ni12P5 shows enhanced performance over Ni2P due to the higher concentration of nickel in this phase, which enables the formation of an amorphous NiOOH/Ni(OH)2 shell on a modified multiphase with a disordered phosphide/phosphite core. The situation is completely reversed in the HER, where Ni2P displayed a significant improvement in electrocatalytic activity over Ni12P5 owing to a larger concentration of phosphide/phosphate species in the shell. Moreover, the efficiently combined use of the two nickel phosphide phases deposited on nickel foam in overall electrocatalytic water splitting is demonstrated by a strikingly low cell voltage and high stability with pronounced current density, and these catalysts could be an apt choice for applications in commercial alkaline water electrolysis. KW - overall water splitting KW - electrocatalysis KW - nickel phosphide KW - structural rearrangement KW - surface structure Y1 - 2017 U6 - https://doi.org/10.1021/acscatal.6b02666 SN - 2155-5435 VL - 7 IS - 1 SP - 103 EP - 109 ER - TY - GEN A1 - Indra, Arindam A1 - Menezes, Prashanth W. A1 - Das, Chittaranjan A1 - Göbel, Caren A1 - Tallarida, Massimo A1 - Schmeißer, Dieter A1 - Driess, Matthias T1 - A facile corrosion approach to the synthesis of highly active CoOxwater oxidation catalysts T2 - Journal of Materials Chemistry A N2 - Ultra-small rock salt cobalt monoxide (CoO) nanoparticles were synthesized and subjected to partial oxidation (‘corrosion’) with ceric ammonium nitrate (CAN) to form mixed-valence CoOx(1 < x< 2) water oxidation catalysts. Spectroscopic, microscopic and analytical methods evidenced a structural reformation of cubic CoO to active CoOx with a spinel structure. The superior water oxidation activity of CoOx has been established in electrochemical water oxidation under alkaline conditions. Electrochemical water oxidation with CoOx was recorded at a considerably low overpotential of merely 325 mV at a current density of 10 mA cm-2 in comparison to 370 mV for CoO. Transformation of both octahedral CoII and CoIII sites into amorphous Co(OH)2–CoOOH is the key to high electrochemical activity while the presence of a higher amount of octahedral CoIII sites in CoOx is imperative for an efficient oxygen evolution process. KW - water splitting KW - water oxidation KW - cobalt oxide catalyst KW - transmission electron microscopy (TEM) KW - X-ray photoelectron spectroscopy (XPS) KW - X-ray absorption spectroscopy (XAS) KW - Cyclic voltammetry (CV) Y1 - 2017 U6 - https://doi.org/10.1039/c6ta10650a SN - 2050-7488 SN - 2050-7496 IS - 5 SP - 5171 EP - 5177 ER - TY - CHAP A1 - Łobaza, Justyna A1 - Kot, Małgorzata A1 - Schmeißer, Dieter T1 - Analysis of surface oxidation of TiON ALD films T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft N2 - Titanium oxynitride (TiON) films are interesting due to their remarkable optical and electronic properties which strongly depend on the O/N ratio. However, it is known that films containing Ti are prone to oxidation in contact with the air [1]. In this work, we study the thickness of a surface oxidation layer which is inherently formed on the atomic layer deposition (ALD) grown TiON/TiN films on Si substrate. We use an Ar+ ion bombardment source and X-ray photoelectron spectroscopy (XPS) for this analysis. We calibrate the sputter rate by using substrate signal intensity decay (here Si 2p) in the XPS spectra of the 5 nm thick TiON sample accordingly. This rate is assumed to be constant when films with a larger thickness are analyzed. We find that the surface oxidation layer is about 1 nm thick, independent on the detailed ALD parameters of the films. The TiN films found underneath are close to the stoichiometric values and have a residual O content below 5%. Finally, we compare these data to our previous results collected with synchrotron-based radiation source [2,3]. References: [1] Sowinska et al., Applied Physics Letters 100, 233509 (2012). [2] M. Sowinska et al., Applied Surface Science 381, 42-47 (2016). [3] M. Sowińska et al., Journal of Vacuum Science and Tech- nology A, 01A12734 (2016). KW - titanium oxynitride KW - X-Rax photoelectron spectroscopy KW - depth profiling KW - sputtering Y1 - 2017 UR - http://www.dpg-verhandlungen.de/year/2017/conference/dresden/part/ds/session/21/contribution/7 SN - 0420-0195 SP - S. 202 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Kot, Małgorzata A1 - Wojciechowski, Konrad A1 - Snaith, Henry J. A1 - Schmeißer, Dieter T1 - Characterization of the perovskite solar cells containing atomic layer deposited Al2O3 buffer layer T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft e.V. N2 - Hybrid perovskites have potential to overcome performance limits of the current solar cell technologies and achieve low cost and high versatility. Nonetheless, they are prone to degradation in presence of moisture within a couple of hours or days. In this work, we use the atomic layer deposition (ALD) of Al2O3 on the CH3NH3PbI3 perovskite at room temperature in order to verify if this thin ALD layer may protect the perovskite film against moisture degradation and to check the impact of the Al2O3 on the solar to power conversion efficiency (PCE). Depth profiling X-ray photoelectron spectroscopy study shows that the ALD precursors are chemically active only at the perovskite surface and the film bulk is not affected. The perovskite film coated with Al2O3 layer has enhanced moisture stability. Solar cells with a fresh-made CH3NH3PbI3 perovskite film have shown PCE of 15.4%, while the one with 50 days aged perovskite only 6.1%. However, when the aged perovskite is covered with RT-ALD-Al2O3 the PCE value is clearly enhanced.[1] [1] M. Kot et al., Room temperature ALD impact on efficiency, stability and surface properties in perovskite solar cells, ChemSusChem,acctepted. KW - Perovskite solar cell KW - atomic layer deposition KW - Al2O3 KW - efficiency recovery Y1 - 2017 UR - http://www.dpg-verhandlungen.de/year/2017/conference/dresden/part/cpp/session/38/contribution/5 SN - 0420-0195 SP - S. 147 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Henkel, Karsten A1 - Kot, Małgorzata A1 - Schmeißer, Dieter T1 - Localized defect states and charge trapping in Al₂O₃ films prepared by atomic layer deposition T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft N2 - The evaluation of the electronic structure and intrinsic defect mechanisms in Al₂O₃ thin films is essential for their effective use in applications with desired functionality such as surface passivation schemes for solar cells [1]. We present a comparative study of different Al₂O₃ films grown by atomic layer deposition (ALD) [2]. The layers were deposited on different substrates using the same aluminum precursor (TMA, trimethylalumium) and employing different process parameters (thermal-ALD, plasma-enhanced-ALD, substrate temperature). These films were characterized by resonant photoelectron spectroscopy and by electrical measurements (capacitance-voltage). For all films investigated intrinsic defect states within the electronic band gap were observed including excitonic, polaronic, and charge-transfer defect states, where their relative abundance is subject of the choice of ALD parameters and of the used substrate. The spectroscopic assigned in-gap defect states are related with electronic charges as determined in the electrical measurements. [1] G. Dingemans and W.M.M. Kessels, J. Vac. Sci. Technol. A 30, 040802 (2012). [2] K. Henkel, M. Kot, D. Schmeißer, J. Vac. Sci. Technol. A 35, (2017), accepted. KW - defect states KW - Al₂O₃ KW - resonant photoelectron spectroscopy KW - X-Ray absorption spectroscopy KW - capacitance-voltage measurements Y1 - 2017 UR - http://www.dpg-verhandlungen.de/year/2017/conference/dresden/part/ds/session/32/contribution/4 SN - 0420-0195 SP - S. 205 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Israel, Johannes A1 - Rachow, Fabian A1 - Schwiertz, Carola A1 - Charlafti, Evgenia A1 - Müller, Klaus A1 - Schmeißer, Dieter T1 - Direct CO2-Methanation of flue gas emitted by conventional power plants T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft N2 - 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. KW - CO2 KW - methanation KW - Sabatier reaction KW - power plant KW - Schwarze Pumpe KW - autothermal mode Y1 - 2017 UR - http://www.dpg-verhandlungen.de/year/2017/conference/muenster/part/ake/session/8/contribution/5 SP - S. 255 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Rachow, Fabian A1 - Hagendorf, Moritz A1 - Müller, Klaus A1 - Schmeißer, Dieter T1 - Synthesis of Methanol from CO2 for Power-to-Liquid applications T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft N2 - 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. KW - direct methanol synthesis KW - power to liquide KW - Cu-ZnO catalyst KW - CO2 utilization Y1 - 2017 UR - http://www.dpg-verhandlungen.de/year/2017/conference/muenster/part/ake/session/8/contribution/5 SP - S. 256 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - GEN A1 - Das, Chittaranjan A1 - Kot, Małgorzata A1 - Rouissi, Zied A1 - Kędzierski, Kamil A1 - Henkel, Karsten A1 - Schmeißer, Dieter T1 - Selective Deposition of an ultrathin Pt Layer on a Au-Nanoisland-Modified Si Photocathode for Hydrogen Generation T2 - ACS Omega N2 - Platinum, being the most efficient and stable catalyst, is used in photoelectrochemical (PEC) devices. However, a minimal amount of Pt with maximum catalytic activity is required to be used to minimize the cost of production. In this work, we use an environmentally friendly, ost-effective, and less Pt-consuming method to prepare PEC devices for the hydrogen evolution reaction (HER). The Pt monolayer catalyst is selectively deposited on a Au-nanoisland-supported boron-doped p-type Si (100) photocathode. The PEC device based on the Si photocathode with an ultralow loading of the Pt catalyst exhibits a comparable performance for the HER to that of devices with a thick Pt layer. In addition, we demonstrate that by using a thin TiO2 layer deposited by atomic layer deposition photo-oxidation of the Si photocathode can be blocked resulting in a stable PEC performance. KW - water splitting KW - hydrogen evolution reaction (HER) KW - Si photocathode KW - gold nanoislands KW - nanostructured platinum Y1 - 2017 U6 - https://doi.org/10.1021/acsomega.6b00374 SN - 2470-1343 VL - 2 IS - 4 SP - 1360 EP - 1366 ER - TY - THES A1 - Israel, Johannes T1 - Sabatierbasierte autothermale katalytische Rauchgasmethanisierung im Technikumsmaßstab und Rückverstromung im BHKW T1 - Sabatier based autothermal catalytic methanation of flue gas in scale of a demonstration plant and reconversion in a CHP N2 - Es konnte gezeigt werden, dass die direkte Methanisierung des Kohlenstoffanteils aus Rauchgas auf Grundlage der Sabatier-Reaktion im Rahmen des Power-to-Gas Ansatzes unter realen Bedingungen im Technikumsmaßstab möglich ist. Es wurde ein Durchsatz von knapp 235 kg/d CO2 bei einer Gesamtraumgeschwindigkeit der Eduktgase von ca. 1500 h-1, was einem Durchfluss von 45 Nm³/h bei einem Reaktorvolumen von 30 dm³ entspricht, erreicht. Dabei wurde das Kohlenstoffdioxid direkt, ohne weitere Aufarbeitung des Rauchgases, mit mindestens 60% Umsatz katalytisch zu Methan reduziert. Dafür wurde ein Katalysator auf Nickelbasis verwendet. Des Weiteren hat sich gezeigt, dass für eine autotherme Betriebsweise der Methanisierung von Rauchgas der Sauerstoffanteil im Rauchgas eine notwendige Voraussetzung darstellt. Es hat sich dabei herausgestellt, dass das vorliegende Intervall von 4 - 6 Vol % Sauerstoffanteil im Rauchgas aus konventionellen Braunkohlekraftwerken genau in dem notwendigen Bereich liegt, der für eine ausgeglichene Wärmebilanz sorgt. Die bei der Wasserstoff-Sauerstoffreaktion zusätzlich frei werdende Wärme gleicht den kühlenden Effekt des mitgetragenen Stickstoffes genau aus, wodurch die für die Sabatier-Reaktion benötigte Temperatur von mindestens 300 °C aufrechterhalten werden kann. Ohne den Sauerstoff könnte die Methanisierung nicht autotherm betrieben werden. Zudem ist die Reaktion selbstregulierend, die Reaktionstemperatur läuft auf einen oberen Grenzwert von etwa 600 °C hinaus, wodurch Umsätze von 60% nicht unterschritten werden. Bei niedrigeren Temperaturen von ca. 400 °C konnten auch Ergebnisse von über 90% CO2 Umsatz im Rauchgas erreicht werden. Diese Ergebnisse konnten sowohl unter Laborbedingungen, d.h. mit aus technischen Gasen synthetisch hergestelltem Rauchgas, gemessen werden, als auch mit realem Rauchgas direkt am Kraftwerk vor Ort reproduziert werden. Das bei der Rauchgasmethanisierung entstehende Produktgas weist eine Energiedichte von ca. 5 MJ/Nm³ auf, womit es zu den Schwachgasen gezählt wird. Hier konnte der Nachweis erbracht werden, dass eine Nutzung des Produktgases in einem Rückverstromungskonzept mittels eines dezentralen Blockheizkraftwerkes, welches mit einem herkömmlichen Wankelmotor betrieben wird, möglich ist. Das "Proof of Principle" für einen geschlossenen CO2 Kreislauf unter realen Bedingungen mittels der Sabatier Reaktion wurde somit erbracht und lädt dazu ein, diesen Weg weiter zu verfolgen. N2 - It is shown, that the direct methanation of the carbon content of flue gas is possible. This was done on the basis of the Sabatier reaction and under real circumstances in a pilot plant scale. At the reactant gases hourly space velocity of approximately 1500 h-1 an output of just under 235 kg/d CO2 was reached, which corresponds to a flow-rate of 45 Nm³/h at a reactor volume of 30 dm³. Without further reprocessing of the flue gas, the carbon dioxide was directly reduced to methane via catalysis, which resulted in a conversion rate of at least 60%. A nickel based catalyst was used. Furthermore, it appeared that the flue gases oxygen content is a necessary precondition for the methanations autothermic mode of operation. Thereby the present interval of 4 - 6 vol% oxygen content of flue gas from conventional lignite power plants turned out to lie exactly in the necessary range to provide an even thermal balance. Since the additionally released heat from the hydrogen-oxygen reaction just compensates for the cooling effect of the present nitrogen, the Sabatier reaction's required temperature of at least 300 °C can be maintained. Without that oxygen the methanation could not be run autothermally. Additionally, the reaction is self-regulating. The reaction temperature results in a maximum limit value of approximately 600 °C, whereby conversion rates do not fall below 60%. At lower temperatures of about 400 °C, results of over 90% CO2 conversion from flue gas could be reached. These results could be measured under laboratory conditions, i.e. with synthetically produced flue gases mixed from industrial gases, and were reproduced with real flue gas directly from the power plant. The resulting gas from the flue gas methanation exhibits an energy density of approximately 5 MJ/Nm³, which ranks it among the lean gases. Here it could be proven that a reconversion of the produced gas into electricity is possible using a local block-type thermal power station, run with a conventional Wankel rotary engine. Thus the 'Proof of Principle' was provided for a closed CO2 circle under real conditions by means of the Sabatier reaction, which is an invitation to further pursue this path. KW - BHKW KW - Blockheizkraftwerk KW - CCU KW - Energiespeicher KW - Kohlendioxid KW - Methanisierung KW - Rauchgas KW - Sabatier KW - Wasserstoff KW - CCU KW - CHP KW - Carbon dioxid KW - Combined heat and power plant KW - Energy storage KW - Flue gas KW - Hydrogen KW - Methanation KW - Power-to-Gas KW - Sabatier Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:co1-opus4-41467 ER - TY - GEN A1 - Kot, Małgorzata A1 - Henkel, Karsten A1 - Das, Chittaranjan A1 - Brizzi, Simone A1 - Kärkkänen, Irina A1 - Schneidewind, Jessica A1 - Naumann, Franziska A1 - Gargouri, Hassan A1 - Schmeißer, Dieter T1 - Analysis of titanium species in titanium oxynitride films prepared by plasma enhanced atomic layer deposition T2 - Surface and Coatings Technology N2 - A comparative study of thin titanium oxynitride (TiOxNy) films prepared by plasma enhanced atomic layer deposition using tetrakis(dimethylamino)titanium (TDMAT) and N2 plasma as well as titanium(IV)isopropoxide and NH3 plasma is reported. The comparison is based on the combination of Ti2p core level and valence band spectroscopy and current-voltage measurements. The TDMAT/N2 process delivers generally higher fractions of TiN and TiON within the Ti2p spectra of the films and stronger photoemissions within the bandgap as resolved in detail by high energy resolution synchrotron-based spectroscopy. In particular, it is shown that higher TiN contributions and in-gap emission intensities correlate strongly with increased leakage currents within the films and might be modified by the process parameters and precursor selection. KW - Titanium oxynitride KW - Plasma enhanced atomic layer deposition (PEALD) KW - ALD process parameters KW - Ti-N contributions KW - In-gap defect states KW - Leakage current Y1 - 2017 U6 - https://doi.org/10.1016/j.surfcoat.2016.11.094 SN - 0257-8972 SN - 1879-3347 VL - 324 SP - 586 EP - 593 ER - TY - THES A1 - Rouissi, Zied T1 - Role of substrate morphology and chemistry in ALD: HfO2 on Si(111)-H terminated surfaces as model N2 - This work presents an approach to investigate fundamental aspects concerning the early stage of the atomic layer deposition (ALD) growth process on stepped surfaces. The first interaction between precursors and surface is strongly important for the ALD growth that it is still far away from the status to be completely understood. For this purpose, a few ALD-cycles with tetrakis(dimethylamido)hafnium (TDMAH) and trimethylaluminum (TMA) as metallic precursors and water (H₂O) as oxidant has been performed in order to study the initial metal oxide film growth on stepped surfaces such as silicon Si(111)-H terminated, highly oriented pyrolytic graphite (HOPG) and silver deposited HOPG (Ag-HOPG). These investigations have been carried out at various substrate temperatures, where scanning tunneling microscopy (STM) has been used systematically to probe the ALD features. This technique is delivering unique knowledge about the locality and the density of nucleation’s sites on the different substrates. The data collected are then subjected to a mathematical model to understand the growth and to determine the effect of the surface morphology and chemistry on the behavior of the nucleation. The in-situ cycle-by-cycle STM investigation of 4 initial ALD cycles of TDMAH and H₂O on Si(111)-H terminated at room temperature (RT) and at 280°C displays two regimes of growth: In Regime I (1st - 2nd cycle) an increase in roughness in the first cycle to 0.2nm and 0.34nm respectively for RT and 280°C with a partial surface coverage of 71% and 54% is observed. In the 2nd cycle, the coverage increased to ~98% and 94% maintaining the same film height of the 1st cycle. A complete layer is formed in this regime. The results are discussed in reference to the Puurunen model. Following this model, the determination of the reaction mechanism in relation to the number of Hf atoms/nm² attached to the surface reveals that two ligands exchanges occur at RT and one ligand exchange at 280°C in the first regime. In addition, the origin of the reaction saturation was determined to be caused by the steric hindrance effect. In this first regime, the growth model is governed by random deposition followed by Mullins diffusion as determined from the universal values found for the roughness dynamic exponents (α, β, 1/z) of the film. N2 - Diese Arbeit beschäftigt sich mit einer Methode, die fundamentalen Aspekte des anfänglichen Schichtwachstums auf gestuften Oberflächen während des Prozesses der Atomlagenabscheidung (ALD) zu untersuchen. Die initiale Wechselwirkung zwischen den Präkursoren und der Oberfläche ist entscheidend für das ALD-Wachstum, wobei diese Wechselwirkung noch nicht komplett verstanden wird. Zu diesem Zweck wurden einige ALD-Zyklen mit Tetrakis(dimethylamido)hafnium (TDMAH) und Trimethylaluminium (TMA) als metallische Präkursoren und Wasser (H₂O) als Oxidant durchgeführt, um das initiale Filmwachstum von Metalloxiden auf gestuften Oberflächen zu untersuchen. Als Oberflächen kamen dabei Wasserstoff-terminiertes Silizium(111), HOPG (HOPG: ‚highly oriented pyrolytic graphite‘) und mit Silber beschichtetes HOPG (Ag-HOPG) zum Einsatz. Diese Untersuchungen wurden an Schichten, die mit verschiedenen Substrattemperaturen gewachsen wurden, durchgeführt, wobei die Methode der Rastertunnelmikroskopie (RTM, englisch STM für ‚scanning tunneling microscopy‘) systematisch angewendet wurde, um die ALD spezifischen Besonderheiten zu erforschen. Diese Technik liefert einzigartige Erkenntnisse über die örtliche Verteilung von Wachstumskeimen und deren Dichte auf verschiedenen Substraten. Die gemessenen Daten wurden anschließend mit einem mathematischen Modell korreliert, um das Wachstum zu verstehen und den Einfluss der Oberflächenmorphologie und –chemie auf das Keimbildungsverhalten zu bestimmen. Die Zyklus für Zyklus durchgeführten in-situ STM-Untersuchungen der ersten 4 ALD-Zyklen von TDMAH und H₂O auf Wasserstoff-terminierten Si(111) bei Raumtemperatur (RT) und 280°C (Substrattemperatur) liefern zwei Wachstumsregimes: Im ersten Regime (I, erster und zweiter ALD-Zyklus) erhöht sich die Oberflächenrauigkeit im ersten Zyklus auf 0,2nm (RT) bzw. 0,34nm (280°C) mit einer partiellen Oberflächenbedeckung von 71% (RT) bzw. 54% (280°C). Nach dem zweiten Zyklus erhöht sich die Oberflächenbedeckung auf 98% (RT) bzw. 94% (280°C), wobei die gleiche Filmdicke wie im ersten Zyklus beibehalten wird. In diesem Regime wird eine komplette Schicht gebildet. Die Ergebnisse wurden auf Basis des Puurunen-Modells diskutiert. Dabei wurde bei der Untersuchung der Reaktionsmechanismen in Abhängigkeit der auf der Oberfläche haftenden Hafnium-Atome (pro nm²) festgestellt, dass im ersten Regime zwei Liganden-Austauschprozesse bei RT und ein Liganden-Austauschprozess bei 280°C stattfinden. Zusätzlich wurde herausgefunden, dass die Reaktionssättigung durch sterische Behinderung determiniert ist. Die Analyse der universellen dynamischen Rauigkeitsexponenten (α, β, 1/z) der Filme führt zum Schluss, dass in diesem ersten Regime das Wachstum durch eine willkürliche Beschichtung gefolgt von der Mullins-Diffusion bestimmt wird. KW - Gestufte Oberfläche KW - Morphologie KW - Rastertunnelmikroskopie (RTM) KW - Wachstumsstatistik KW - Atomlagenabscheidung (ALD) KW - Atomic layer deposition (ALD) KW - Growth statistics KW - Morphology KW - Scanning tunneling microscopy (STM) KW - Stepped surface Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:co1-opus4-42418 UR - https://opus4.kobv.de/opus4-btu/frontdoor/index/index/docId/4241 PB - BTU Cottbus-Senftenberg CY - Cottbus ER - TY - GEN A1 - Indra, Arindam A1 - Menezes, Prashanth W. A1 - Das, Chittaranjan A1 - Schmeißer, Dieter A1 - Driess, Matthias T1 - Alkaline electrochemical water oxidation with multi-shelled cobalt manganese oxide hollow spheres T2 - Chemical Communications N2 - Multi-shelled hollow spheres of cobalt manganese oxides (CMOs) deposited on Ni foam exhibited superior alkaline electrochemical water oxidation activity and surpassed those of bulk CMO and commercial noble metal-based catalysts. A higher amount of cobalt in the spinel structure resulted in the transformation of the tetragonal to the cubic phase with a decrease in the overpotential of oxygen evolution. KW - Water oxidation KW - Cobalt manganese oxides (CMOs) KW - Multi-shelled hollow spheres KW - Near-edge X-ray absorption fine structure (NEXAFS) KW - Cyclic voltammetry KW - Scanning electron microscopy Y1 - 2017 U6 - https://doi.org/10.1039/C7CC03566G SN - 1359-7345 SN - 1364-548X VL - 53 IS - 62 SP - 8641 EP - 8644 ER - TY - GEN A1 - Biswas, Anirban A1 - Henkel, Karsten A1 - Schmeißer, Dieter A1 - Mandal, Dipankar T1 - Comparison of the thermal stability of the α, β and γ phases in poly(vinylidene fluoride) based on in situ thermal Fourier transform infrared spectroscopy T2 - Phase Transitions N2 - The electroactive β phase of poly(vinylidenefluoride) (PVDF) is induced due to the aging time of PVDF solutions. The feasibility of the combination of the three crystalline polymorphs (α, β and γ) is demonstrated where their relative proportion within the PVDF film can be tailored by the simple monitoring of the preparation conditions. To identify all these phases, Fourier transform infrared (FT-IR) spectroscopy is carried out and it is spotlighted that the vibrational bands at 510 and 841 cm-1 are not sufficient to state the formation of the β phase. The main aim of this work is devoted to develop a better understanding on the thermal stability of these several phases of PVDF, which has a longstanding ambiguity persisting in this area. It has been found that the in situ thermal FT-IR spectroscopy is one of the best alternatives to understand this important issue. It is ascertained that the β phase is the least thermally stable phase among α, β and γ phases, whereas the γ phase is the most thermally stable phase. KW - PVDF KW - thermal stability KW - β-phase KW - infrared spectroscopy KW - in situ thermal FT-IR study Y1 - 2017 U6 - https://doi.org/10.1080/01411594.2017.1337902 SN - 0141-1594 SN - 1029-0338 VL - 90 IS - 12 SP - 1205 EP - 1213 ER - TY - GEN A1 - Cibrev, Dejan A1 - Tallarida, Massimo A1 - Das, Chittaranjan A1 - Lana-Villarreal, Teresa A1 - Schmeißer, Dieter A1 - Gómez, Roberto T1 - New insights into water photooxidation on reductively pretreated hematite photoanodes T2 - Physical Chemistry Chemical Physics N2 - It has been recently demonstrated that the photoactivity toward oxygen evolution of a number of n-type metal oxides can be substantially improved by a reductive electrochemical pretreatment. Such an enhancement has been primarily linked to the formation of low valent metal species that increase electrode conductivity. In this work, we report new insights into the electrochemical doping using highly ordered (110)-oriented hematite nanorods directly grown on FTO. The reductive pretreatment consists in applying negative potentials for a controlled period of time. Such a pretreatment was optimized in both potentiostatic and potentiodynamic regimes. We show that the optimized pretreatment enhances electrode conductivity due to an increase in charge carrier density. However, it additionally triggers changes in the morphologic, catalytic and electronic properties that facilitate the separation and collection of the photogenerated charge carriers causing an up to 8-fold enhancement in the photocurrent for water oxidation. The reductive pretreatment can be considered as a highly controllable electrochemical n-type doping with the amount of generated Fe2+/polaron species and the change in film morphology as the main factors determining the final efficiency for water photooxidation of the resulting electrodes. KW - hematite KW - photoanode KW - water oxidation KW - water splitting Y1 - 2017 U6 - https://doi.org/10.1039/C7CP03958A SN - 1463-9076 SN - 1463-9084 VL - 19 IS - 32 SP - 21807 EP - 21817 ER - TY - THES A1 - Rachow, Fabian T1 - Prozessoptimierung für die Methanisierung von CO₂ – vom Labor zum Technikum N2 - In dieser Arbeit konnte gezeigt werden, dass eine direkte Methanisierung von CO₂, die über die Sabatier-Gleichung, CO₂ + 4H₂ ↔ CH₄ + 2H₂O, beschrieben wird, im Labor- und im Technikums-Maßstab unter Variation verschiedenster Bedingungen realisierbar ist. Die Sabatier-Reaktion findet beschleunigt unter dem Einsatz von Katalysatoren statt. Unterschiedliche kommerzielle Katalysatoren auf Nickel und Ruthenium-Basis konnten auf ihrer Eignung für die Methanisierung untersucht werden und mit im Labor präparierte Katalysatoren verglichen werden. Relevante Größen zur Beschreibung der Aktivität der Katalysatoren ist der Umsatz an CO₂, die Ausbeute an CH₄ und die Selektivität bezüglich der Sabatier-Reaktion. Im Labor wurden Umsätze und Ausbeuten von über 90% und Selektivitäten von nahezu 100% gemessen. Durch eine Änderung der Temperatur, der Eingangsmenge an Gasen, der Katalysatormenge und des Druckes können die optimalen Prozessbedingungen für die Reaktion spezifiziert werden. Eine weitere Betrachtung galt der Messung mit synthetischen und realen Abgasen (Oxyfuel, CCS) und darauf bezogen, der Einfluss einer Verdünnung des CO₂ durch Stickstoff und Sauerstoff und der Rolle von bekannten Katalysatorgiften wie Schwefel- oder Stickoxiden. Es konnte ein Zusammenhang zwischen der Stärke der Verunreinigung an Schwefel, der Reaktortemperatur und der Abnahme der katalytischen Aktivität ermittelt werden. Die Produktion von Kohlenmonoxid gibt zusätzlich Aufschluss über stattfinden Teil-und Nebenreaktionen. Ergebnisse in der Laboranlage konnten zum Teil für den Aufbau einer Technikumsanlage, welche eine Vergrößerung zum Labor um den Faktor 5000 darstellt, genutzt werden. Eine Zahl von Experimenten wurde im Technikum wiederholt. Die Technikumsanlage ist dabei in der Lage ca. 250 kg CO₂ pro Tag aus CO₂-haltigen Abgasen in Methan umzuwandeln. Ein erweiterter Praxisbezug stellte die Einbindung des Technikums in einem Kraftwerk dar und die Messung mit realem Rauchgas. Ohne zusätzliche Reinigungsschritte des Abgases konnten auch hier Umsätze von 90% erreicht werden. Eine komplexe Temperaturentwicklung und Erhöhung auf 600°C im Reaktor wurde aufgezeichnet und führt dabei zur Abnahme des Umsatzes auf ca. 60%. Bei diesen Temperaturen stellt sich ein Gleichgewicht zwischen, durch die exotherme Reaktion, erzeugter und abgeführter Wärme ein. Als Reaktionsprodukt wird ein Schwachgas erhalten, welches für die Rückverstromung eingesetzt werden kann. In der Methanisierung von CO₂ besteht die Möglichkeit das CO₂ in einen Kreislauf (Power-to-Gas) zu binden und so die Emission von Treibhausgasen zu mindern. Das erzeugte Methan fungiert als chemischer Energiespeicher und trägt zur Stabilisierung des Stromnetzes bei. N2 - It could be shown, that the direct methanation of CO₂, as described by the Sabatier-reaction, CO₂ + 4H₂ ↔ CH₄ + 2H₂O, can be done in laboratory and in an industrial scale under a variation of different process parameters. The Sabatier reaction is accelerated by catalysts. Different commercially available nickel and ruthenium-based catalysts were reviewed for their use in methanation and compared with self-prepared catalysts. Relevant parameters for the activity of a catalyst are the conversion of CO₂, the yield of CH₄ and the selectivity regarding the Sabatier-reaction. A conversion and yield of above 90% and a selectivity of nearly 100% were measured in the laboratory-set-up. Optimal parameters for the process were studied by variation of temperature, quantity of the reactants, amount of catalyst and pressure inside the reactor. An additional approach was the reaction with synthetic and real flue gases (Oxyfuel, CCS) and in this regard, a dilution of the CO₂ with nitrogen and oxygen and the role of known contaminations like sulfur and nitrogen oxides that can poison the catalyst. A relation between the amount of sulfur contamination, the temperature and the decrease in activity could be determined. It was possible to discern single reaction mechanism due to the formation of carbon monoxide during the reaction. Results in the laboratory have been used for the construction of a pilot-plant that represents an upscale of 5000 in gas quantity. A number of experiments were repeated in the pilot-plant. Here, it was possible to convert nearly 250kg/day CO₂ from flue gases to methane. The pilot plant was integrated into a power plant and therefore measurements with real flue gas could be conducted. Without additional cleaning of the flue gas, a conversion rate of up to 90% was achieved. A complex temperature distribution and an increase in the temperature of the reactor up to 600°C lead to a decrease in conversion to 60%. Equilibrium between the produced and removed heat is reached at those temperatures. The resulting gas has a low energy density and is classified as a lean gas that could be used for a reconversion to electric power. The methanation of CO₂ represents a possibility to store the CO₂ into a loop of conversion and reconversion of energy (Power-to-Gas) and therefore it is possible to reduce the emission of greenhouse gases. The produced methane is a chemical energy storage and contributes to the stabilization of the electric grid. KW - CO2-Nutzung KW - Energiespeicher KW - Erneuerbare Energien KW - Katalyse KW - Methanisierung KW - Carbon capture and storage (CCS) KW - Catalysis KW - Energy storage KW - Renewable energy KW - Methanation Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:co1-opus4-42625 CY - Cottbus ER - TY - GEN A1 - Kot, Małgorzata A1 - Das, Chittaranjan A1 - Henkel, Karsten A1 - Wojciechowski, Konrad A1 - Snaith, Henry J. A1 - Schmeißer, Dieter T1 - Room temperature atomic layer deposited Al₂O₃ on CH₃NH₃PbI₃ characterized by synchrotron-based X-ray photoelectron spectroscopy T2 - Nuclear Instruments and Methods in Physics Research B N2 - An ultrathin Al₂O₃ film deposited on methylammonium lead triiodide (CH₃NH₃PbI₃) perovskite has the capability to suppress the carrier recombination process and improve the perovskite solar cells efficiency and stability. However, annealing at temperatures higher than 85°C degrades the CH₃NH₃PbI₃ perovskite film. The X-ray photoelectron spectroscopy study performed in this work indicates that it is possible to grow Al₂O₃ by atomic layer deposition on the perovskite at room temperature, however, besides pure Al₂O₃ some OH groups are found and the creation of lead and iodine oxides at the Al₂O₃/CH₃NH₃PbI₃ interface takes place. KW - Synchrotron-based X-ray photoelectron spectroscopy KW - Perovskite solar cells KW - Atomic layer deposition KW - Al₂O₃ Y1 - 2017 U6 - https://doi.org/10.1016/j.nimb.2017.01.082 SN - 0168-583X SN - 1872-9584 VL - 411 SP - 49 EP - 52 ER - TY - GEN A1 - Schmeißer, Dieter A1 - Janowitz, Christoph T1 - Two polarization dependent Auger decays observed by resonant photoelectron spectroscopy at the Cu2p-edge of superconducting BiSrCu-oxides T2 - Nuclear Instruments and Methods in Physics Research B N2 - We report on a resonant photoemission (resPES) study of PbxBi2-xSr2-yLayCan-1CunO2n+4+d (BISCO) single crystals to unravel the resonant decay mechanisms at the Cu2p absorption edge. The resPES studies on superconducting BISCO are performed at Bessy U49/2. We investigated BISCO single crystals with different hole doping concentrations at temperatures between 300 K and 17 K. CuO films have been used as a reference. We focus on the resPES data recorded at the Cu2p absorption edge. We find a strong polarization dependence for in-plane and out-of-plane geometries (with respect to the Cu-O plane) in our data which are caused by two independent Auger processes. We also report on the influence of different doping concentrations. Our resPES data enable us to sort the individual resonant mechanisms at the Cu2p edge in more detail than recently anticipated (Brookes et al., 2015). We discuss our data in the context of the recent discussion about the applicability of the Zhang-Rice model (Chen et al., 2013). KW - Synchrotron radiation KW - Superconductor KW - Cuprates KW - Resonant photoemission Y1 - 2017 U6 - https://doi.org/10.1016/j.nimb.2017.01.084 SN - 0168-583X SN - 1872-9584 VL - 411 SP - 53 EP - 56 ER - TY - GEN A1 - Müller, Klaus A1 - Bär, Werner A1 - Henkel, Karsten A1 - Jahnke, Agnes A1 - Schwiertz, Carola A1 - Schmeißer, Dieter T1 - Organische Feldeffekttransistoren als Transducer in der Biosensorik T1 - Organic Field Effect Transistors as Biosensors T2 - Technisches Messen N2 - In diesem Beitrag wird der Einsatz neuartiger Sensortypen für die medizinische Diagnostik beschrieben. Diese Sensoren sollen komplett organisch sein und auf dem Prinzip des Feldeffekttransistors basieren. Als Modellsystem für die Anwendung in der Biosensorik soll die Einsatzmöglichkeit dieser Sensoren in der nicht-invasiven Diagnostik der Helicobacter-pylori-Infektion überprüft werden. N2 - In this contribution we describe the investigation of new types of sensors in medical diagnosis. These sensors are completely organic and are based on the principle of organic field effect transistors. As model system for application in medical diagnosis we test the usability of this sensors for the diagnosis of helicobacter pylori. KW - Feldeffekttransistor KW - Biosensorik KW - Helicobacter pylori KW - Field effect transistors KW - biosensors KW - helicobacter pylori Y1 - 2003 U6 - https://doi.org/10.1524/teme.70.12.565.20261 SN - 0171-8096 VL - 70 IS - 12 SP - 565 EP - 568 ER - TY - GEN A1 - Müller, Klaus A1 - Rachow, Fabian A1 - Israel, Johannes A1 - Charlafti, Evgenia A1 - Schwiertz, Carola A1 - Schmeißer, Dieter T1 - Direct Methanation of Flue Gas at a Lignite Power Plant T2 - International Journal of Environmental Science N2 - 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. KW - CO2 recycling KW - Power to Gas (PtG) KW - Synthetic Natural Gas (SNG) KW - Sabatier-Reaction KW - Flue Gas Y1 - 2017 UR - http://www.iaras.org/iaras/home/caijes/direct-methanation-of-flue-gas-at-a-lignite-power-plant SN - 2367-8941 IS - 2 SP - 425 EP - 437 ER - TY - GEN A1 - Kot, Małgorzata A1 - Łobaza, Justyna A1 - Naumann, Franziska A1 - Gargouri, Hassan A1 - Henkel, Karsten A1 - Schmeißer, Dieter T1 - Long-term ambient surface oxidation of titanium oxynitride films prepared by plasma-enhanced atomic layer deposition: An XPS study T2 - Journal of Vacuum Science and Technology A N2 - The surface oxidation of a titanium oxynitride (TiOxNy) film after long-time storage of 25 month in ambient conditions is investigated. The TiOxNy film is prepared by plasma-enhanced atomic layer deposition using etrakis(dimethylamino)titanium and nitrogen plasma, and the film is characterized by Ar+ ion sputtering of the film surface in combination with x-ray photoelectron spectroscopy (XPS) as well as by angle-resolved XPS. The total thickness of an oxygen-enriched layer at the surface of the TiOxNy films is found to be about 0.7 nm and it consists of a sequence of a 0.4 nm thick TiON/TiO2 enriched layer followed by a 0.3 nm thick TiO2 enriched layer underneath compared to the bulk composition of the film which shows constant values of 29% TiN, 29% TiO2, and 42% TiON. The results suggest that the TiON enrichment takes place initially at the surface followed by a surface and subsurface oxidation. KW - atomic layer deposition (ALD) KW - surface oxidation KW - X-Ray photoelectron spectroscopy (XPS) KW - titanium oxynitride Y1 - 2018 U6 - https://doi.org/10.1116/1.5003356 SN - 0734-2101 SN - 1520-8559 VL - 36 IS - 1 ER - TY - GEN A1 - Schmeißer, Dieter A1 - Henkel, Karsten T1 - Intrinsic defects and multiple-atom processes in the oxidic semiconductor Ga₂O₃ T2 - Journal of Applied Physics N2 - We report on the electronic structure of gallium oxide (Ga₂O₃) single crystals as studied by resonant photoelectron spectroscopy (resPES). We identify intrinsic electronic defects that are formed by mixed-atomic valence states. We differentiate three coexisting defect states that differ in their electronic correlation energy and their spatial localization lengths. Their relative abundance is described by a fractional ionicity with covalent and ionic bonding contributions. For Ga₂O₃, our analyses of the resPES data enable us to derive two main aspects: first, experimental access is given to determine the ionicity based on the original concepts of Pauling and Phillips. Second, we report on multi-atomic energy loss processes in the Ga2p core level and X-ray absorption data. The two experimental findings can be explained consistently in the same context of mixed-atomic valence states and intrinsic electronic defects. KW - resonat photoelectron spectroscopy (resPES) KW - X-Ray absorption KW - gallium oxide (Ga₂O₃) KW - intrinsic electronic defects KW - band scheme Y1 - 2018 U6 - https://doi.org/10.1063/1.5010740 SN - 0021-8979 SN - 1089-7550 VL - 123 IS - 16 SP - 161596-1 EP - 161596-9 ER - TY - GEN A1 - Kot, Małgorzata A1 - Wojciechowski, Konrad A1 - Snaith, Henry J. A1 - Schmeißer, Dieter T1 - Evidence of Nitrogen Contribution to the Electronic Structure of the CH₃NH₃PbI₃ Perovskite T2 - Chemistry - A European Journal N2 - Despite fast development of hybrid perovskite solar cells, there are many fundamental questions related to the perovskite film which remain open. For example, there are contradicting theoretical reports on the role of the or-ganic methylammonium cation (CH₃NH₃+)in the methylam-monium lead triiodide (CH₃NH₃PbI₃)perovskite film. From one side it is reported that the organic cation does not contribute to electronic structure of the CH₃NH₃PbI₃ film. From the other side, valence band maximum fluctuations, dependent on the CH₃NH₃+ rotation, have been theoretically predicted. The resonant X-ray photoelectron spectroscopy results reported here show experimental evidence of nitrogen contribution to the CH₃NH₃PbI₃ electronic structure. Moreover,the observed strong resonances of nitrogen with the I 5s and the Pb 5d-6s levels indicate that the CH₃NH₃PbI₃ valence band is extended up to ~18 eV below the Fermi energy, and therefore one should also consider these shallow core levels while modeling its electronic structure. KW - methylammonium lead triiodide (CH₃NH₃PbI₃) KW - electronic structure KW - perovskite solar cells KW - resonant X-ray photoelectron spectroscopy (resPES) Y1 - 2018 U6 - https://doi.org/10.1002/chem.201705144 SN - 0947-6539 SN - 1521-3765 VL - 24 IS - 14 SP - 3539 EP - 3544 ER - TY - GEN A1 - Janowitz, Christoph A1 - Schmeißer, Dieter T1 - Significance of out-of-plane electronic contributions in Bi-cuprates studied by resonant photoelectron spectroscopy at the Cu2p-edge T2 - Superconductor Science and Technology N2 - In high-temperature superconductors with a layered crystal structure, the copper–oxygen planes are commonly considered to dominate the electronic properties around the Fermi energy. As a consequence, out-of-plane contributions are often neglected in the description of these materials. Here we report on a resonant photoemission study of Pb₀,4Bi1,₆Sr₂,₀CaCu₂0₈ ((Pb, Bi)-2212) and Pb₀,₆Bi₁,₄Sr₁.5La₀.5Cu0₆ ((Pb, Bi)-2201)) single crystals to unravel the resonant decay mechanisms at the Cu2p absorption edge. We find evidence for a pronounced polarization dependence caused by two different Auger processes for in-plane and out-of-plane orientations. We deduce that the lowest energy valence state—which is involved in the two Auger processes—consists of three-dimensional contributions by admixed out-of-plane Sr, Bi, and 02p states. It also suggests that the doping-induced charge density is dynamic, fluctuating within the Cu–0 plane, and spills out perpendicular to it. This suggests that out-of-plane electronic degrees of freedom should be included in future consistent theoretical models of these materials. KW - synchrotron radiation KW - polarization dependence KW - 3D hole doping KW - superconductor Y1 - 2018 U6 - https://doi.org/10.1088/1361-6668/aaadf6 SN - 0953-2048 SN - 1361-6668 VL - 31 IS - 4 ER - TY - CHAP A1 - Garain, Samiran A1 - Henkel, Karsten A1 - Mandal, Dipankar A1 - Schmeißer, Dieter T1 - One-Pot Synthesis of Copper Oxide Nanowires and PVDF/CuO Composite Films for Piezoelectric Energy Harvesting Application T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Band 53,3 N2 - Copper oxide (CuO) is an attractive p-type oxide semiconductor with narrow band gap that has intriguing properties such as non-toxicity, chemical stability, electrocatalytic activity, abundant availability and low production cost. Polymeric materials have attracted great interest owing to their high flexibility, light weight, low cost production and high resistance against corrosion. Poly(vinylidene fluoride) (PVDF) is a commonly used piezoelectric polymer due to its excellent flexibility and piezoelectric properties. In this work, we adopted a one-pot synthesis of CuO nanowires by facile and selective chemical etching process of Cu substrate. XPS, XRD, SEM data ascribed the formation of polycrystalline CuO nanowires over the entire Cu surface. It has been observed that the uniformity, shape and size of the nanowires could be conveniently controlled by etching time and etchant concentration. We have also prepared piezoelectric nanogenerator based on the flexible PVDF/CuO composite film, where the traditional electrical poling treatment was avoided. In addition, dielectric properties have been studied to demonstrate the role of interfacial polarization. KW - PVDF KW - electroactive phase KW - nanogenerators KW - energy storage Y1 - 2018 UR - https://www.dpg-verhandlungen.de/year/2018/conference/berlin/part/cpp/session/20/contribution/21 SN - 0420-0195 SP - S. 135 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Kot, Małgorzata A1 - Naumann, Franziska A1 - Garain, Samiran A1 - Poźarowska, Emilia A1 - Gargouri, Hassan A1 - Henkel, Karsten A1 - Schmeißer, Dieter T1 - Aluminum nitride films prepared by plasma atomic layer deposition using different plasma sources T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Band 53,3 N2 - Aluminum nitride (AlN) thin films are promising for versatile applications in optoelectronics, electronics, piezoelectrics, and acoustics due to their remarkable properties such as wide band gap, high dielectric constant, low electrical conductivity, good piezoelectric coefficient and high ultrasonic velocity. We present a comparative study of AlN films grown by plasma-enhanced atomic layer deposition at 350°C silicon wafers in the SENTECH SI ALD LL system using TMA and NH3 where either a capacitively coupled plasma (CCP) or a direct PTSA (planar triple spiral antenna) source was applied. The films were characterized by ellipsometry, XPS and electrical measurements. The layer properties are discussed concerning the varied ALD process parameters. In general, the process using the direct PTSA source delivered films with higher refractive index and better homogeneity over the wafer achieving also higher growth rates per cycle (GPC) in reduced total cycle durations. Films with refractive index in the range of 2.05 and permittivity around 8 could be realized with a GPC of 1.54 Å/cycle. KW - Aluminium nitride KW - plasma-enhanced atomic layer deposition (PEALD) KW - ellispsometry KW - field emission scanning electron microscopy KW - atomic force microscopy KW - X-ray photoelectron spectroscopy KW - electrical characterization Y1 - 2018 SN - 0420-0195 SP - S. 170 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Kot, Małgorzata A1 - Kegelmann, Lukas A1 - Kus, Peter A1 - Tsud, Nataliya A1 - Matolínová, Iva A1 - Albrecht, Steve A1 - Matolin, Vladimir A1 - Schmeißer, Dieter T1 - Room temperature atomic layer deposition for perovskite solar cells T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Band 53,3 N2 - After few years of efficiency driven research on perovskite solar cells, the focus now is shifting to understand the underlying processes governing the high efficiency and also to obtain long-term stable devices. Among various deposition methods, atomic layer deposition (ALD) may represent one of the best options, being possible to coat substrates in a very efficient way and at very low temperatures. In our previous work [1] we reported that the efficiency of the solar cell containing aged perovskite film can be enhanced twice while covering the perovskite with a thin ALD alumina film at room temperature. In this work, the chemical, electronic and morphological properties of the fresh perovskite film treated by ALD pulses of the trimethylaluminium and water at room temperature investigated using X-ray Photoelectron Spectroscopy and Field Emission Scanning Electron Microscopy will be discused and correlated with the solar cells performance and stability. [1] M. Kot et al., ChemSusChem 2016, 9, 3401. KW - Perovskite solar cells KW - atomic layer deposition KW - X-Ray photoelectron spectroscopy (XPS) KW - atomic force microscopy KW - field emission scanning electron microscopy KW - photo-conversion efficiency Y1 - 2018 SN - 0420-0195 SP - S. 174 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - GEN A1 - Garain, Samiran A1 - Sen, Shrabanee A1 - Henkel, Karsten A1 - Schmeißer, Dieter A1 - Mandal, Dipankar T1 - Enhancement of Electroactive β-phase and Superior Dielectric Properties in Cerium Based Poly(vinylidene fluoride) Composite Films T2 - Materials Today: proceedings N2 - In this work we report on the preparation of poly(vinylidene fluoride) (PVDF) films with various mass fractions (wt%) of hydrated rare earth metal salt [(NH4)4Ce(SO4)4.2H2O] (CAS) and its electroactive phase (β- and γ-phase) formation. It was found that CAS can yield high amount of electroactive phases in PVDF. Compared to the neat PVDF film, a significantly increment of dielectric constant (ε ∼ 41) and a low loss factor (tan δ ∼ 0.8) were observed in the PVDF-CAS composite films. Thus the PVDF-CAS composite films with high electroactive phase and superior dielectric properties may meet the requirements of next generation electronic components. KW - PVDF KW - High amount of electroactive phase KW - Superior dielectric properties Y1 - 2018 U6 - https://doi.org/10.1016/j.matpr.2017.11.003 SN - 2214-7853 VL - 5 IS - 3 part 3 SP - 10084 EP - 10090 ER - TY - CHAP A1 - Henkel, Karsten A1 - Kot, Małgorzata A1 - Richter, Matthias A1 - Tallarida, Massimo A1 - Schmeißer, Dieter ED - Wandelt, Klaus T1 - An (In Situ)² Approach: ALD and resPES Applied to Al₂O₃, HfO₂, and TiO₂ Ultrathin Films T2 - Encyclopedia of Interfacial Chemistry: Surface Science and Electrochemistry, Vol. 3.1 N2 - Oxide surface coatings are of importance in tailoring interface properties with respect to surface passivation, adjustment of surface potentials, or providing active centers for surface reactions. In this contribution, we report about surface coatings prepared by the atomic layer deposition (ALD) method. ALD is known for its conformal growth of ultrathin, dense films which exhibit a low concentration of pinholes. KW - Atomic layer deposition (ALD) KW - Resonant photoelectron spectroscopy (resPES) KW - Band scheme KW - Partial density of states (pDOS) KW - Intrinsic charges KW - Intrinsic defects KW - Aluminum oxide (Al₂O₃) KW - Hafnium oxide (HfO₂) KW - Titanium oxide(TiO₂) Y1 - 2018 SN - 978-0-12-809739-7 SN - 978-0-12-809894-3 U6 - https://doi.org/10.1016/B978-0-12-409547-2.13852-1 SP - 18 EP - 26 PB - Elsevier CY - Oxford ER - TY - CHAP A1 - Schmeißer, Dieter A1 - Kot, Małgorzata A1 - Corrêa, Silma Alberton A1 - Das, Chittaranjan A1 - Henkel, Karsten ED - Wandelt, Klaus T1 - Interface Potentials, Intrinsic Defects, and Passivation Mechanisms in Al₂O₃, HfO₂, and TiO₂ Ultrathin Films T2 - Encyclopedia of Interfacial Chemistry: Surface Science and Electrochemistry, vol. 3.1 N2 - We study the electronic structure of ultrathin Al₂O₃, HfO₂, and TiO₂ ALD films by resonant photoelectron spectroscopy. We identify intrinsic defects which are responsible for the active sites in interface reactions, for the incorporation of intrinsic charges, and for the formation of local dipole momenta. All of these features determine the surface potentials and the reactivity of the surface of the atomic layer deposition coated systems. We give examples of charges and dipoles in Al₂O₃, on a study of the surface potentials in HfO₂, and relate the intrinsic defects in TiO₂ to their electrochemical relevance. KW - Atomic layer deposition (ALD) KW - Resonant photoelectron spectroscopy (resPES) KW - Band scheme KW - Interface potential KW - Intrinsic charges KW - Intrinsic defects KW - Partial density of states (pDOS) KW - Exciton KW - Polaron KW - Ligand-to-metal charge transfer KW - Aluminium oxide (Al₂O₃) KW - Hafnium oxide (HfO₂) KW - Titanium Oxide (TiO₂) Y1 - 2018 SN - 978-0-12-809739-7 SN - 978-0-12-814984-3 U6 - https://doi.org/10.1016/B978-0-12-409547-2.14119-8 SP - 162 EP - 171 PB - Elsevier CY - Oxford ER - TY - GEN A1 - Brinkert, Katharina A1 - Richter, Matthias A1 - Akay, Ömer A1 - Liedtke, Janine A1 - Giersig, Michael A1 - Fountaine, Katherine T. A1 - Lewerenz, Hans-Joachim T1 - Efficient Solar Hydrogen Generation in Microgravity Environment T2 - Nature Communications N2 - Long-term space missions require extra-terrestrial production of storable, renewable energy. Hydrogen is ascribed a crucial role for transportation, electrical power and oxygen generation. We demonstrate in a series of drop tower experiments that efficient direct hydrogen production can be realized photoelectrochemically in microgravity environment, providing an alternative route to existing life support technologies for space travel. The photoelectrochemical cell consists of an integrated catalyst-functionalized semiconductor system that generates hydrogen with current densities >15 mA/cm2 in the absence of buoyancy. Conditions are described adverting the resulting formation of ion transport blocking froth layers on the photoelectrodes. The current limiting factors were overcome by controlling the micro- and nanotopography of the Rh electrocatalyst using shadow nanosphere lithography. The behaviour of the applied system in terrestrial and microgravity environment is simulated using a kinetic transport model. Differences observed for varied catalyst topography are elucidated, enabling future photoelectrode designs for use in reduced gravity environments. Y1 - 2018 U6 - https://doi.org/10.1038/s41467-018-04844-y SN - 2041-1723 IS - 9 ER - TY - GEN A1 - Brinkert, Katharina A1 - Richter, Matthias A1 - Akay, Ömer A1 - Giersig, Michael A1 - Fountaine, Katherine T. A1 - Lewerenz, Hans-Joachim T1 - Advancing semiconductor-electrocatalyst systems: application of surface transformation films and nanosphere lithography T2 - Faraday Discussions N2 - Photoelectrochemical (PEC) cells offer the possibility of carbon-neutral solar fuel production through artificial photosynthesis. The pursued design involves technologically advanced III–V semiconductor absorbers coupled via an interfacial film to an electrocatalyst layer. These systems have been prepared by in situ surface transformations in electrochemical environments. High activity nanostructured electrocatalysts are required for an efficiently operating cell, optimized in their optical and electrical properties. We demonstrate that shadow nanosphere lithography (SNL) is an auspicious tool to systematically create three-dimensional electrocatalyst nanostructures on the semiconductor photoelectrode through controlling their morphology and optical properties. First results are demonstrated by means of the photoelectrochemical production of hydrogen on p-type InP photocathodes where hitherto applied photoelectrodeposition and SNL-deposited Rh electrocatalysts are compared based on their J–V and spectroscopic behavior. We show that smaller polystyrene particle masks achieve higher defect nanostructures of rhodium on the photoelectrode which leads to a higher catalytic activity and larger short circuit currents. Structural analyses including HRSEM and the analysis of the photoelectrode surface composition by using photoelectron spectroscopy support and complement the photoelectrochemical observations. The optical performance is further compared to theoretical models of the nanostructured photoelectrodes on light scattering and propagation. KW - shadow nanosphere lithography (SNL) KW - electrocatalyst nanostructures KW - Rh electrocatalysts KW - InP photocathodes Y1 - 2018 U6 - https://doi.org/10.1039/C8FD00003D SN - 1359-6640 SN - 1364-5498 VL - 208 SP - 523 EP - 535 ER - TY - GEN A1 - Schmeißer, Dieter A1 - Henkel, Karsten A1 - Janowitz, Christoph T1 - Ionicity of ZnO - a key system for transparent conductive oxides T2 - epl : a letters journal exploring the frontiers of physics N2 - The electronic structure of ZnO is dominated by coexisting electron and ionic states/bonds caused by charge polarization and self-trapping phenomena of the valence charges. Their interplay manifests itself in intrinsic electronic defects which have different degree of spatial localization and electronic correlation. The relative abundance of intrinsic defects can be determined by the ionicity factor fi and its value can be derived from three independent experimental procedures in a consistent way. This approach also explains the complex satellite features in the XPS and XAS data. Ionicity and satellite formation are two experimental findings which can be explained consistently in the same context of mixed-atomic valence states and intrinsic electronic defects. KW - Ionicity KW - zinc oxide (ZnO) KW - resonant photoelectron spectroscopy KW - defect states KW - transparent conductive oxide (TCO) Y1 - 2018 U6 - https://doi.org/10.1209/0295-5075/123/27003 SN - 1286-4854 SN - 0295-5075 VL - 123 IS - 2 SP - 27003-p1 EP - 27003-p7 ER - TY - GEN A1 - Kot, Małgorzata A1 - Kegelmann, Lukas A1 - Das, Chittaranjan A1 - Kus, Peter A1 - Tsud, Nataliya A1 - Matolínová, Iva A1 - Albrecht, Steve A1 - Matolin, Vladimir A1 - Schmeißer, Dieter T1 - Room temperature atomic layer deposited Al₂O₃ improves perovskite solar cells efficiency over time T2 - ChemSusChem N2 - Electrical characterisation of perovskite solar cells consisting of room-temperature atomic-layer-deposited aluminium oxide (RT-ALD-Al₂O₃) film on top of a methyl ammonium lead triiodide (CH₃NH₃PbI₃) absorber showed excellent stability of the power conversion efficiency (PCE) over along time. Under the same environmental conditions (for 355 d), the average PCE of solar cells without the ALD layer decreased from 13.6 to 9.6 %, whereas that of solar cells containing 9 ALD cycles of depositing RT-ALD-Al₂O₃on top of CH₃NH₃PbI₃ increased from 9.4 to 10.8 %. Spectromicroscopic investigations of the ALD/perovskite interface revealed that the maximum PCE with the ALD layer is obtained when the so-called perovskite cleaning process induced by ALD precursors is complete. The PCE enhancement over time is probably related to a self-healing process induced by the RT-ALD-Al₂O₃ film. This work may provide a new direction for further improving the long-term stability and performance of perovskite solar cells. KW - Perovskite Solar Cells (PSCs) KW - Atomic layer deposition (ALD) KW - long time stabilty KW - X-Ray photoelectron spectroscopy (XPS) KW - Field-emission scanning electron microscopy (FESEM) Y1 - 2018 U6 - https://doi.org/10.1002/cssc.201801434 SN - 1864-5631 SN - 1864-564X VL - 11 IS - 20 SP - 3640 EP - 3648 ER - TY - CHAP A1 - Henkel, Karsten A1 - Haeberle, Jörg A1 - Müller, Klaus A1 - Janowitz, Christoph A1 - Schmeißer, Dieter ED - Fornari, Robert T1 - Preparation, properties and electronic structure of SnO₂ T2 - Single Crystals of Electronic Materials N2 - 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. KW - electronic structure KW - tin oxide (SnO₂) KW - resonant photoelectron spectroscopy KW - intrinsic defect states Y1 - 2018 SN - 978-0-08-102096-8 SN - 978-0-08-102097-5 SP - 547 EP - 572 PB - Elsevier, Woodhead Publishing CY - Duxford ER - TY - GEN A1 - Maity, Kuntal A1 - Garain, Samiran A1 - Henkel, Karsten A1 - Schmeißer, Dieter A1 - Mandal, Dipankar T1 - Natural Sugar-Assisted, Chemically Reinforced, Highly Durable Piezoorganic Nanogenerator with Superior Power Density for Self-Powered Wearable Electronics T2 - ACS Applied Materials & Interfaces N2 - Natural piezoelectric materials are of increasing interest, particularly for applications in biocompatible, implantable, and flexible electronic devices. In this paper, we introduce a cost-effective, easily available natural piezoelectric material, that is, sugar in the field of wearable piezoelectric nanogenerators (PNGs) where low electrical output, biocompatibility, and performance durability are still critical issues. We report on a high-performance piezoorganic nanogenerator (PONG) based on the hybridization of sugar-encapsulated polyvinylidenefluoride (PVDF) nanofiber webs (SGNFW). We explore the crucial role of single-crystal sugar having a fascinating structure along with the synergistic enhancement of piezoelectricity during nanoconfinement of sugar-interfaced macromolecular PVDF chains. As a consequence, the SGNFW-based PONG exhibits outstanding electricity generation capability (e.g.,∼100 V under 10 kPa human finger impact and maximum power density of 33 mW/m2) in combination with sensitivity to abundantly available different mechanical sources (such as wind flow, vibration, personal electronics, and acoustic vibration). Consequently, it opens up suitability in multifunctional self-powered wearable sensor designs for realistic implementation. In addition, commercially available capacitors are charged up effectively by the PONG because of its rapid energy storage capability. The high performance of the PONG not only offers“battery-free”energy generation (several portable units of light-emitting diodes and a liquid crystal display screen are powered up without using external storage) but also promises its use in wireless signal transmitting systems, which widens the potential in personal health care monitoring. Furthermore, owing to the geometrical stress confinement effect, the PONG is proven to be a highly durable power-generating device validated by stability test over 10 weeks. Therefore, the organic nanogenerator would be a convenient solution for portable personal electronic devices that are expected to operate in a self-powered manner. KW - natural piezoelectric material KW - sugar KW - PVDF KW - organic piezoelectric nanogenerator KW - high performance and durability KW - self-powered electronics Y1 - 2018 U6 - https://doi.org/10.1021/acsami.8b15320 SN - 1944-8244 SN - 1944-8252 VL - 10 SP - 44018 EP - 44032 ER - TY - GEN A1 - Bignardi, Luca A1 - Lizzit, Daniel A1 - Bana, Harsh A1 - Travaglia, Elisabetta A1 - Lacovig, Paolo A1 - Sanders, Charlotte E. A1 - Dendzik, Maciej A1 - Michiardi, Matteo A1 - Bianchi, Marco A1 - Ewert, Moritz A1 - Buß, Lars A1 - Falta, Jens A1 - Flege, Jan Ingo A1 - Baraldi, Alessandro A1 - Larciprete, Rosanna A1 - Hofmann, Philip A1 - Lizzit, Silvano T1 - Growth and structure of singly oriented single-layer tungsten disulfide on Au(111) T2 - Physical Review Materials N2 - A singly oriented, single layer of tungsten disulfide (WS2) was epitaxially grown on Au(111) and characterized at the nanoscale by combining photoelectron spectroscopy, photoelectron diffraction, and low-energy electron microscopy. Fast x-ray photoelectron spectroscopy revealed that the growth of a single crystalline orientation is triggered by choosing a low W evaporation rate and performing the process with a high temperature of the substrate. Information about the single orientation of the layer was obtained by acquiring x-ray photoelectron diffraction patterns, revealing a 1H polytype for the WS2 layer and, moreover, determining the structural parameters and registry with the substrate. The distribution, size, and orientation of the WS2 layer were further ascertained by low-energy electron microscopy. KW - tungsten disulfide (WS2) KW - Au (111) KW - photoelectron spectroscopy KW - photoelectron diffraction KW - low-energy electron microscopy Y1 - 2019 U6 - https://doi.org/10.1103/PhysRevMaterials.3.014003 SN - 2475-9953 VL - 3 IS - 1 ER - TY - GEN A1 - Flege, Jan Ingo A1 - Höcker, Jan A1 - Sadowski, Jerzy T. A1 - Senanayake, Sanjaya D. A1 - Falta, Jens T1 - Nucleation, morphology, and structure of sub‐nm thin ceria islands on Rh(111) T2 - Surface and Interface Analysis N2 - The early stages of ceria growth on Rh(111) at high temperature have been investi-gated by low‐energy electron microscopy and photoemission electron microscopy. Ceria was deposited by reactive Ce deposition at substrate temperatures between 700°C and 900°C in an oxygen ambient of 5 × 10−7 Torr. At 700°C, we observe a high nucleation density of 100‐nm‐sized islands. With elevated temperature, the average island size increases, and the nucleation density decreases. Triangularly shaped islands nucleate preferentially at step edges, with seemingly abrupt interfaces between Ce and Rh. At 900°C, the island edges are still straight, but during growth the islands lose their triangular form. Instead, growth along the substrate step edges becomes favorable, leading to a maze‐like morphology. Atomic force microscopy reveals islands of 0.3 to 0.6‐nm height, consistent with ceria islands formed by one or two trilayers (O―Ce―O) of ceria. Moreover, the second layer of the islands is also triangularly shaped, with lateral dimensions of 50 nm and similar step heights. IV‐LEEM analysis leads to the conclusion that the rhodium surface is covered by a layer of reduced cerium oxide, which is partially overgrown by smaller islands of CeO2. KW - ceria KW - Rh (111) KW - low‐energy electron microscopy (LEEM) KW - photoemission electron microscopy (PEEM) KW - IV-LEEM Y1 - 2019 U6 - https://doi.org/10.1002/sia.6567 SN - 0142-2421 SN - 1096-9918 VL - 51 IS - 1 SP - 110 EP - 114 ER - TY - GEN A1 - Biswas, Anirban A1 - Garain, Samiran A1 - Maity, Kuntal A1 - Henkel, Karsten A1 - Schmeißer, Dieter A1 - Mandal, Dipankar T1 - Influence of In situ Synthesized Bismuth Oxide Nanostructures in Self-poled PVDF-based Nanogenerator for Mechanical Energy Harvesting Application T2 - Polymer Composites N2 - A self-poled piezoelectric nanogenerator (NG) based on bismuth oxide (Bi2O3) nanostructures (BNS)-doped poly(vinylidene fluoride) (PVDF) is demonstrated. The in-situ formation of BNS incorporated in the PVDF matrix is realized through a simple solution casting technique that favors the nucleation and stabilization of 99.6% of the electroactive phase in PVDF (i.e., beta/gamma-phases). The enhancement of the output voltage (3.6 V) and current (2.4mA) of the NG based on a nonelectrically poled BNS containing PVDF composite film is achieved and demonstrated by simple repeated human finger imparting. The improvement of the output performance is influenced by the generation of the electroactive polar beta-phase in PVDF, due to the electrostatic interactions between the –CH2–/–CF2– dipoles of PVDF and the surface charge of the BNS. The NGs are able to charge up capacitors demonstrating that the power generation from such a hybrid device structure can be utilized for powering various portable devices. KW - Nanogenerators KW - energy harvesting KW - PVDF KW - bismuth oxide KW - Field-emission scanning electron microscopy (FESEM) KW - X-ray photoelectron spectroscopy (XPS) KW - X-ray diffraction (XRD) KW - Fourier Transform Infrared Spectroscopy (FTIR) Y1 - 2019 U6 - https://doi.org/10.1002/pc.24628 SN - 0272-8397 SN - 1548-0569 VL - 40 IS - S1 SP - E265 EP - E274 ER - TY - GEN A1 - Kot, Małgorzata A1 - Henkel, Karsten A1 - Naumann, Franziska A1 - Gargouri, Hassan A1 - Tarnawska, Lidia Lupina A1 - Wilker, Viola A1 - Kus, Peter A1 - Pożarowska, Emilia A1 - Garain, Samiran A1 - Rouissi, Zied A1 - Schmeißer, Dieter T1 - Comparison of plasma-enhanced atomic layer deposition AlN films prepared with different plasma sources T2 - Journal of Vacuum Science and Technology A N2 - A comparative study of thin aluminum nitride (AlN) films deposited by plasma-enhanced atomic layer deposition in the SENTECH SI ALD LL system applying either a direct inductively coupled plasma (ICP) or an indirect capacitively coupled plasma (CCP) source is presented. The films prepared with the ICP source (based on a planar triple spiral antenna) exhibit improved properties concerning the growth rate per cycle, total cycle duration, homogeneity, refractive index, fixed and mobile electrical charges, and residual oxygen content compared to the CCP source, where the comparison is based on the applied plasma power of 200 W. The increase of the plasma power to 600 W in the ICP process significantly reduces the residual oxygen content and enhances the electrical breakdown field. The AlN layers grown under these conditions, with a growth rate per cycle of 1.54 Å/cycle, contain residual oxygen and carbon concentrations of about 10% and 4%, respectively, and possess a refractive index of 2.07 (at 632.8 nm). KW - Plamsa-enhanced atomic layer deposition (PEALD) KW - inductively coupled KW - capacitively coupled KW - plamsa source KW - ellipsometry KW - X-ray photoelectron spectroscopy (XPS) KW - X-ray diffraction (XRD) KW - Field emission scanning electron microscopy (FESEM) KW - capacitance-voltage (CV) KW - atomic force microscopy Y1 - 2019 U6 - https://doi.org/10.1116/1.5079628 SN - 0734-2101 SN - 1520-8559 VL - 37 IS - 2 ER - TY - GEN A1 - Kotwica, Tomasz A1 - Domaradzki, Jarosław A1 - Wojcieszak, Damian A1 - Sikora, Andrzej A1 - Kot, Małgorzata A1 - Schmeißer, Dieter T1 - Analysis of surface properties of Ti-Cu-Ox gradient thin films using AFM and XPS investigations T2 - Materials Science-Poland N2 - The paper presents results of investigations on surface properties of transparent semiconducting thin films based on (Ti-Cu)oxide system prepared using multi-magnetron sputtering system. The thin films were prepared using two programmed profiles of pulse widt hmodulation coefficient, so called V- and U-shape profiles. The applied powering profiles allowed fabrication of thin films with gradient distribution of Ti and Cu elements over the thickness of deposited layers. Optical investigations allowed determination of transparency of prepared films that reached up to 60 % in the visible part of optical radiation, which makes them attractive for the transparent electronics domain. Surface properties investigations showed that the surface of mixed (Ti-Cu)oxides was sensitive to adsorption, in particular to carbon dioxide and water vapor. Soft etching with argon ions resulted in surface cleaning from residuals, however, deoxidation of Cu-oxide components was also observed. KW - surface KW - gradient distribution KW - thin film oxide Y1 - 2019 U6 - https://doi.org/10.2478/msp-2018-0100 SN - 0137-1339 SN - 2083-1331 SN - 2083-134X VL - 36 IS - 4 SP - 761 EP - 768 ER - TY - GEN A1 - Luches, Paola A1 - Gasperi, Gabriele A1 - Sauerbrey, Marc A1 - Valeri, Sergio A1 - Falta, Jens A1 - Flege, Jan Ingo T1 - Dynamics of the Interaction Between Ceria and Platinum During Redox Processes T2 - Frontiers in Chemistry N2 - The work is focused on understanding the dynamics of the processes which occur at the interface between ceria and platinum during redox processes, by investigating an inverse catalytic model system made of ceria epitaxial islands and ultrathin films supported on Pt(111). The evolution of the morphology, structure and electronic properties is analyzed in real-time during reduction and oxidation, using low-energy electron microscopy and spatially resolved low-energy electron diffraction. The reduction is induced using different methods, namely thermal treatments in ultra-high vacuum and in H2 as well as deposition of Ce on the oxide surface, while re-oxidation is obtained by exposure to oxygen at elevated temperature. The use of two different epitaxial systems, continuous films and nanostructures, allows determining the influence of platinum proximity on the stabilization of the specific phases observed. The factors that limit the reversibility of the observed modifications with the different oxidation treatments are also discussed. The obtained results highlight important aspects of the cerium oxide/Pt interaction that are relevant for a complete understanding of the behavior of Pt/CeO2 catalysts. KW - cerium oxide KW - platinum KW - low‐energy electron microscopy (LEEM) KW - low-energy electron diffraction (LEED) KW - reduction Y1 - 2019 U6 - https://doi.org/10.3389/fchem.2019.00057 SN - 2296-2646 VL - 7 ER - TY - GEN A1 - Schmidt, Thomas A1 - Ahrens, Christian A1 - Flege, Jan Ingo A1 - Jaye, Cherno A1 - Fischer, Daniel A. A1 - Falta, Jens T1 - Growth of Epitaxial 3,4,9,10-Perylene Tetracarboxylic Dianhydride on Bi-Terminated Silicon T2 - Journal of Physical Chemistry C N2 - The epitaxial quality of thin films crucially depends on their interaction with the substrate. Up to now, Ag-terminated Si(111) has been employed as the model substrate for the growth of 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) on semiconductors. In this study, we will show that Bi termination results in PTCDA films of superior epitaxial quality. We have studied the growth of PTCDA on bismuth-passivated Si(111) in detail by means of spot profile analysis of low-energy electron diffraction (SPA-LEED), X-ray photoemission spectroscopy (XPS), near-edge X-ray absorptionfine structure (NEXAFS), and scanning tunneling microscopy (STM). The XPS results reveal the presence of intact PTCDA molecules on the surface upon adsorption. NEXAFS data indicate the PTCDA molecules being oriented with their molecular plane parallel to the surface. STM shows a very smooth growth front of the PTCDA film, preserving the step structure of the substrate. High-resolution SPA-LEED data demonstrate the presence of a multidomain surface with a rich variety of PTCDA surface structures, which were identified to be most prominently herring-bone polytypes. However, in the monolayer range, quadratic brick-wall structures and a nearly square-like structure as well as a perylene-like structure have also been found. Despite the simultaneous presence of multiple domains, the individual domains show excellent lateral ordering, with larger domain sizes as compared to the case of Ag-terminated Si(111). KW - dianhydride KW - Bi-terminated silicon KW - spot profile analysis of low-energy electron diffraction (SPA-LEED) KW - X-ray photoemission spectroscopy (XPS) KW - near-edge X-ray absorptionfine structure (NEXAFS) KW - scanning tunneling microscopy (STM) Y1 - 2019 U6 - https://doi.org/10.1021/acs.jpcc.8b10396 SN - 1932-7447 SN - 1932-7455 VL - 123 IS - 12 SP - 7097 EP - 7109 ER - TY - GEN A1 - Buß, Lars A1 - Falta, Jens A1 - Flege, Jan Ingo T1 - Intercalation dynamics of sulfur underneath graphene on Ru(0001) T2 - Verhandlungen der DPG N2 - It is known that the binding of epitaxially grown graphene to the substrate has a detrimental effect on its electronic properties. This is especially true for the strong binding to various transition metals and particularly ruthenium. However, via intercalation the interlayer coupling can be lifted and its unique electronic properties can be restored. Therefore, we have investigated the interaction of sulfur with single-layer graphene grown on Ru(0001) via surface segregation and CVD of ethylene under UHV conditions with in situ low-energy electron microscopy (LEEM) and micro-diffraction (µLEED). At elevated temperature and under dimethyl disulfide background pressure, we observe that sulfur intercalates through the open edges of the graphene islands. Prolonged exposure to sulfur induces wrinkling of the graphene islands, consistent with substantial relief of tensile strain after successful sulfur insertion underneath the graphene. It can be seen that the intercalation dynamics are both dependent on the temperature during intercalation and the preparation method of the graphene sheets. Furthermore, darkfield imaging and µLEED of the intercalated graphene reveal a graphene induced improved ordering of sulfur underneath. KW - low-energy electron microscopy (LEEM) KW - micro-diffraction (µLEED) Y1 - 2019 UR - https://www.dpg-verhandlungen.de/year/2019/conference/regensburg/part/o/session/7/contribution/9 SN - 0420-0195 SP - 315 EP - 315 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - GEN A1 - Ewert, Moritz A1 - Buß, Lars A1 - Moras, Paolo A1 - Falta, Jens A1 - Flege, Jan Ingo T1 - Unraveling the growth mechanism of single-domain molybdenum disulfide on Au(111) T2 - Verhandlungen der DPG N2 - As a transition metal dichalcogenide single-layer molybdenum disulfide (MoS2) is a heavily investigated system. Due to its direct band gap, the electronic properties of single-layer MoS2 have been subject to several surface science methods. A well-known model system is MoS2 on Au(111). We present in situ low-energy electron microscopy (LEEM) and micro-diffraction (LEED) observations of MoS2 growth on Au(111) at elevated temperature using two distinctly different deposition rates. Our investigations reveal similar but different expansion mechanisms of the MoS2 islands changing a balanced distribution of the two mirror domains towards a single domain distribution. Structural characterization by I(V)-LEEM and investigations of the electronic bandstructure using angle-resolved photoelectron spectroscopy both confirm single-layer nature of the MoS2 islands. We could identify step pushing of the growing MoS2 being responsible for this phenomena. KW - low-energy electron microscopy (LEEM) KW - micro-diffraction (LEED) KW - I(V)-LEEM KW - investigations of the electronic bandstructure using angle-resolved photoelectron spectroscopy Y1 - 2019 UR - https://www.dpg-verhandlungen.de/year/2019/conference/regensburg/part/o/session/35/contribution/6 SN - 0420-0195 SP - 329 EP - 329 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - GEN A1 - Janowitz, Christoph A1 - Schmeißer, Dieter T1 - Out-of-plane electronic contributions in Bi-cuprates studied by resonant photoelectron spectroscopy at the Cu 2p edge T2 - Verhandlungen der DPG N2 - In high-temperature superconductors with a layered crystal structure out-of-plane contributions are often neglected, while the copper-oxygen planes are commonly considered to dominate the electronic properties around the Fermi energy. Here we report on a resonant photoemission study of (Pb,Bi)2201 and (Pb,Bi)2212 single crystals to unravel the resonant decay mechanisms at the Cu 2p absorption edge. We demonstrate a pronounced polarization dependence caused by two different Auger processes for in-plane and out-of-plane orientations. We deduce that the lowest energy valence state being involved in the two Auger processes, consists of three-dimensional contributions by admixed out-of-plane Sr, Bi, and O 2p states. It also suggests that the doping-induced charge density is dynamic, fluctuating within the Cu-O plane, and spills out perpendicular to it. C. Janowitz and D. Schmeißer, Supercond. Sci. Technol. 31, 045006 (2018) KW - high-temperature superconductors KW - resonant photoemission spectroscopy KW - single crystal KW - doping-induced charge density Y1 - 2019 UR - https://www.dpg-verhandlungen.de/year/2019/conference/regensburg/part/tt/session/49/contribution/19 SN - 0420-0195 SP - 403 EP - 403 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER -