@misc{MuellerStaedterRachowetal., author = {M{\"u}ller, Klaus and St{\"a}dter, Matthias and Rachow, Fabian and Hoffmannbeck, David and Schmeißer, Dieter}, title = {Sabatier-based CO2-methanation by catalytic conversion}, series = {Environmental Earth Sciences}, volume = {70}, journal = {Environmental Earth Sciences}, number = {8}, issn = {1866-6280}, doi = {10.1007/s12665-013-2609-3}, pages = {3771 -- 3778}, abstract = {The catalytic conversion of CO2is an important component for the reintegration of secondary products like CO2 or H2 into the energy supply. An example is the "power to gas'" concept with a conversion of CO2 into CH4. The CO2 is transferred into a carrier of chemical energy, with the possibility to feed the produced CH4 into the existing network of natural gas. At temperatures of around 350 °C, hydrogenation of CO2 to CH4 is possible by the Sabatier reaction CO2+4H2->CH4+H2O. One prerequisite for efficient kinetics of the Sabatier reaction is the application and optimization of catalysts. The focus of catalyst development is given to their performance under the conditions to be expected in the special application. As a part of the project Geoenergy-Research (GeoEn), we address questions related to the catalytic utilization of CO2 produced in the course of the oxyfuel combustion of lignite. In this contribution, we report on the experimental setup in laboratory scale, which enables an advanced characterization of the catalytic performance, including thermodesorption measurements at atmospheric pressure in order to determine the amount of adsorbed CO2 under real conditions. We also show data for activation energies, the catalytic performance as function of temperature and the long time stability of a commercial Ru-based catalyst.}, language = {en} } @misc{DasTallaridaSchmeisser, author = {Das, Chittaranjan and Tallarida, Massimo and Schmeißer, Dieter}, title = {Linear dichroism in ALD layers of TiO₂}, series = {Environmental Earth Sciences}, volume = {70}, journal = {Environmental Earth Sciences}, number = {8}, issn = {1866-6280}, doi = {10.1007/s12665-013-2836-7}, pages = {3785 -- 3795}, abstract = {We prepare TiO₂film by ALD and study their electronic properties by soft X-ray absorption spectroscopy (XAS) and photoelectron spectroscopy. We focus on XAS and X-ray linear dichroism to indentify band onset and learn about local distortion of the Ti-O octahedral atomic and about defects which cause Ti-based electronic states within the band gap.}, language = {en} } @misc{StaedterMuellerRachowetal., author = {St{\"a}dter, Matthias and M{\"u}ller, Klaus and Rachow, Fabian and Richter, Matthias and Schmeißer, Dieter}, title = {Ambient pressure thermal desorption spectroscopy (AP-TDS) of NiO/SiO2 catalysts}, series = {Environmental Earth Sciences}, volume = {70}, journal = {Environmental Earth Sciences}, number = {8}, issn = {1866-6280}, doi = {10.1007/s12665-013-2835-8}, pages = {3779 -- 3784}, abstract = {The Sabatier reaction is a key process in the "power-to-gas" application which is considered to con-tribute to future chemical energy storage systems. In this contribution we focus on the catalytic active sites of a NiO catalyst supported on SiO2(NiO/SiO2) which is commonly used in the Sabatier reaction. A novel technique for the characterization of the active sites is presented and dis-cussed using thermal desorption spectroscopy at ambient pressure. This analytical tool is operated under reaction conditions and allows element specific measurements during the catalytic process of CO2 reforming towards methane. Beside the desorption experiments, XPS and XAS measurements of pristine and catalytically used samples are performed to determine the influence of the Sabatier reaction conditions on the surface structure of the catalyst.}, language = {en} } @misc{ScheckWenderothSchmeisserMuttietal., author = {Scheck-Wenderoth, Magdalena and Schmeißer, Dieter and Mutti, Maria and Kolditz, Olaf and Huenges, Ernst and Schultz, Hans-Martin and Liebscher, Axel and Bock, Michaela}, title = {Geoenergy: new concepts for utilization of geo-reservoirs as potential energy sources}, series = {Environmental Earth Sciences}, volume = {70}, journal = {Environmental Earth Sciences}, number = {8}, issn = {1866-6280}, doi = {10.1007/s12665-013-2877-y}, pages = {3427 -- 3431}, language = {en} } @misc{GerlichOhsiekKleinetal., author = {Gerlich, Lukas and Ohsiek, Susanne and Klein, Christoph and Geiß, Mario and Friedemann, Michael and K{\"u}cher, Peter and Schmeißer, Dieter}, title = {Interface engineering for the TaN/Ta barrier film deposition process to control Ta-crystal growth}, series = {Microelectronic Engineering}, volume = {Vol. 106}, journal = {Microelectronic Engineering}, doi = {10.1016/j.mee.2013.01.017}, pages = {63 -- 68}, abstract = {As a consequence of device shrinking the resistivity of the widely used TaN/Ta double barrier layer becomes an increasingly important parameter for device speed beyond the 32 nm technology node. In this study we describe the optimization of the deposition of TaN/Ta stacks in such a way that tantalum nitride layer thickness is minimized and tantalum grows in the favorable conducting alpha-phase. In the first part of the study we usedin situ ARXPS to investigate the growth of different tantalum nitride layers on SiO2 and SiOCH as a function of deposition time, nitrogen flow and deposition power. In the second part we analyzed the crystalline phase of a 20 nm thick tantalum layer deposited on top of the same series of tantalum nitride layers characterized in the growth study. The main findings are the appearance of tan-talum carbide and tantalum silicide as interface species for the deposition on SiOCH and only tantalum silicide for the deposition on SiO2. We found that alpha-tantalum grows preferably on tantalum carbide and nitrogen rich intermediate layers whereas silicide at the interface promotes the growth of beta-tantalum. To verify these findings we studied two additional modifications of the interface. A lower bias power for a deposition of tantalum nitride on SiO2 was used to confirm the role of tantalum silicide and a thermal treatment of a thin tantalum layer on SiOCH was applied to confirm the role of tantalum carbide. Finally, the contact resistance in via chains on patterned wafers for four selected processes showed the same trends as the sheet resistance of the corresponding barrier films on blanket wafer experiments.}, language = {en} } @misc{HenkelGargouriGruskaetal., author = {Henkel, Karsten and Gargouri, Hassan and Gruska, Bernd and Arens, Michael and Tallarida, Massimo and Schmeißer, Dieter}, title = {Capacitance and conductance versus voltage characterization of Al2O3 layers prepared by PE-ALD at 25°C ≤ T ≤ 200°C}, series = {Journal of Vacuum Science and Technology A}, volume = {1}, journal = {Journal of Vacuum Science and Technology A}, number = {32}, doi = {10.1116/1.4831897}, pages = {01A107-1 -- 01A107-10}, abstract = {In this work, plasma enhanced atomic layer deposited (PE-ALD) samples were prepared at substrate temperatures in the range between room temperature (RT) and 200 °C and investigated by capacitance-voltage and conductance-voltage recordings. The measurements are compared to standard thermal atomic layer deposition (T-ALD) at 200 °C. Very low interface state density (D it) ~1011 eV-1 cm-2 could be achieved for the PE-ALD process at 200 °C substrate temperature after postdeposition anneal (PDA) in forming gas at 450 °C. The PDA works very effectively for both the PE-ALD and T-ALD at 200 °C substrate temperature delivering also similar values of negative fixed charge density (N fix) around -2.5 × 1012 cm-2. At the substrate temperature of 150 °C, highest N fix (-2.9 × 1012 cm-2) and moderate D it (2.7 × 1011 eV-1 cm-2) values were observed. The as deposited PE-ALD layer at RT shows both low D it in the range of (1 to 3) × 1011 eV-1 cm-2 and low N fix (-4.4 × 1011 cm-2) at the same time. The dependencies of N fix, D it, and relative permittivity on the substrate temperatures and its adjustability are discussed.}, language = {en} } @phdthesis{Hoffmann, author = {Hoffmann, Patrick}, title = {Untersuchungen zu Inhomogenit{\"a}ten an der Halbleitergrenzfl{\"a}che Silizium-Siliziumoxynitrid}, publisher = {Shaker-Verlag}, address = {Aachen}, isbn = {3-8322-1982-X}, pages = {179}, language = {de} } @phdthesis{Mikalo, author = {Mikalo, Ricardo Pablo}, title = {Elektronische Eigenschaften von leitf{\"a}higen konjugierten Polymeren und deren Grenzfl{\"a}chenreaktionen im elektrischen Kontakt mit Metallen}, publisher = {Der Andere Verlag}, address = {Osnarbr{\"u}ck}, isbn = {3-89959-115-1}, pages = {310, XIII}, language = {de} } @phdthesis{Heller, author = {Heller, Thomas}, title = {Molekulare Resonanzen im Wirkungsquerschnitt der Photoemission in den Valenzzust{\"a}nden der st{\"o}chiometrischen und der mit Natrium belegten WO3 und TiO2 (110) 1x1 Oberfl{\"a}che}, publisher = {Shaker}, address = {Aachen}, isbn = {3-8322-0742-2}, pages = {157}, language = {de} } @phdthesis{Yfantis, author = {Yfantis, Alexandros D.}, title = {Development and Characterisation of Corrosion Resistent Layers of Conducting Polymers on Aluminium Alloys}, publisher = {Parissianou}, address = {Athen}, isbn = {960-394-115-8}, pages = {XI, 103}, language = {en} } @phdthesis{Appel, author = {Appel, G{\"u}nter}, title = {Untersuchungen zur mesoskopischen und elektronischen Struktur von Polypyrroltosylat und Polypyrrolkupferphthalocyaninsulfonat}, publisher = {Shaker}, address = {Aachen}, isbn = {3-8265-4830-2}, pages = {118}, language = {de} } @phdthesis{Hofmann, author = {Hofmann, Andreas}, title = {Elektronische Struktur epitaktischer Chalkopyrite und deren Heterokontakte f{\"u}r die Photovoltaik}, address = {Cottbus}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus-24434}, pages = {194}, language = {de} } @phdthesis{Zimmer, author = {Zimmer, Fabian}, title = {Herstellung und Charakterisierung hocheffzienter, mikromechanischer NIR-Beugungsgitter f{\"u}r den Einsatz in miniaturisierten Spektrometern}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus-25224}, pages = {XVI, 127}, language = {de} } @phdthesis{Dudek, author = {Dudek, Piotr T.}, title = {Atomic scale engineering of HfO2-based dielectrics for future DRAM applications}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus-22775}, pages = {106}, abstract = {Modern dielectrics in combination with appropriate metal electrodes have a great potential to solve many difficulties associated with continuing miniaturization process in the microelectronic industry. One significant branch of microelectronics incorporates dynamic random access memory (DRAM) market. The DRAM devices scaled for over 35 years starting from 4 kb density to several Gb nowadays. The scaling process led to the dielectric material thickness reduction, resulting in higher leakage current density, and as a consequence higher power consumption. As a possible solution for this problem, alternative dielectric materials with improved electrical and material science parameters were intensively studied by many research groups. The higher dielectric constant allows the use of physically thicker layers with high capacitance but strongly reduced leakage current density. This work focused on deposition and characterization of thin insulating layers. The material engineering process was based on Si cleanroom compatible HfO2 thin films deposited on TiN metal electrodes. A combined materials science and dielectric characterization study showed that Ba added HfO2 (BaHfO3) films and Ti added BaHfO3 (BaHf0.5Ti0.5O3) layers are promising candidates for future generation of state of the art DRAMs. In especial a strong increase of the dielectric permittivity k was achieved for thin films of cubic BaHfO3 (k~38) and BaHf0.5Ti0.5O3 (k~90) with respect to monoclinic HfO2 (k~19). Meanwhile the CET values scaled down to 1 nm for BaHfO3 and ~0.8 nm for BaHf0.5Ti0.5O3 with respect to HfO2 (CET=1.5 nm). The Hf4+ ions substitution in BaHfO3 by Ti4+ ions led to a significant decrease of thermal budget from 900°C for BaHfO3 to 700°C for BaHf0.5Ti0.5O3. Future studies need to focus on the use of appropriate metal electrodes (high work function) and on film deposition process (homogeneity) for better current leakage control.}, language = {en} } @phdthesis{Rauscher, author = {Rauscher, Stefan}, title = {Dynamische Modifizierung von Silizium-Elektrolyt-Grenzfl{\"a}chen und deren oberfl{\"a}chenphysikalischen Eigenschaften}, publisher = {Brandenburgische Techn. Univ.}, address = {Cottbus}, pages = {185}, language = {de} } @misc{RichterStarkeSchmeisser, author = {Richter, Matthias and Starke, Ulrich and Schmeißer, Dieter}, title = {Multiple Auger processes in Graphene}, series = {Journal of Electron Spectroscopy and Related Phenomena}, journal = {Journal of Electron Spectroscopy and Related Phenomena}, number = {Vol. 192}, issn = {0368-2048}, doi = {10.1016/j.elspec.2013.12.009}, pages = {1 -- 6}, abstract = {Resonant Auger decay processes have been studied by resonant photoemission spectroscopy (resPES) and X-ray absorption spectroscopy (XAS) in Graphene systems. The pi*-resonance is used to identify the degree of localization of the lowest pi*-orbitals in the conduction band. Localization and lifetime of the photo-excited intermediate state cause the formation of multiple Auger processes. For the Graphene systems we identify two novel Auger decay combinations with a four hole final state: the (S+S) and the(S+S)* decay. We demonstrate that these processes are sensitive for interlayer coupling and interactions with the metallic free electrons of the substrate.}, language = {en} } @misc{TallaridaDasSchmeisser, author = {Tallarida, Massimo and Das, Chittaranjan and Schmeißer, Dieter}, title = {Quantum size effects in TiO2 thin films grown by atomic layer deposition}, series = {Beilstein Journal of Nanotechnology}, journal = {Beilstein Journal of Nanotechnology}, number = {5}, issn = {2190-4286}, doi = {10.3762/bjnano.5.7}, pages = {77 -- 82}, abstract = {We study the atomic layer deposition of TiO2 by means of X-ray absorption spectroscopy. The Ti precursor, titanium isopropoxide, was used in combination with H2O on Si/SiO2 substrates that were heated at 200 °C. The low growth rate (0.15 {\AA}/cycle) and the in situ characterization permitted to follow changes in the electronic structure of TiO2 in the sub-nanometer range, which are influenced by quantum size effects. The modified electronic properties may play an important role in charge carrier transport and separation, and increase the efficiency of energy conversion systems.}, language = {en} } @misc{RichterFriedrichSchmeisser, author = {Richter, Matthias and Friedrich, Daniel and Schmeißer, Dieter}, title = {Interlayer-exciton mediated three-hole-Auger-decay in the pi-band of highly oriented pyrolytic graphite}, series = {Physica E}, volume = {Vol. 56}, journal = {Physica E}, issn = {1386-9477}, doi = {10.1016/j.physe.2013.01.015}, pages = {441 -- 446}, abstract = {Resonant photoemission spectroscopy(resPES) is used to probe the occupied pi- and unoccupied pi*-bands of carbon thin films with particular focus on the Auger decay. Highly Oriented Pyrolytic Graphite (HOPG) is studied at the C1s edge. We find strong resonant features at 285.5 eV and 292 eV in the resPES diagram. The normal two-hole Auger decay proceeds under constant kinetic energy (451)only in the sigma*-region. In the pi*-region, however, it proceeds under 67.5° in terms of a Ebind(w) diagram. We attribute this to a multiple Auger decay with a net three hole final state. For this novel decay process we propose a model.We discuss the long lifetime of the first resonant excitation and conclude that it arises from the strong excitonic character of the first resonant state. We use HOPG as a reference system and suggest that this novel process is a tool to identify interlayer-substrate interaction of the carbon layers involved.}, language = {en} } @phdthesis{Michling, author = {Michling, Marcel Frank}, title = {Spektroskopische Untersuchungen an organischen Materialien und Metalloxiden}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus-29014}, pages = {181}, abstract = {Im Rahmen der vorliegenden Arbeit wurde mit Synchrotron-basierenden, optischen und Elektronen-basierenden Methoden die elektronischen Eigenschaften zweier unterschiedlicher Materialklassen untersucht. Der Fokus lag dabei im besonderen auf der Bestimmung der Gr{\"o}ße der Bandl{\"u}cke/HOMO-LUMO-L{\"u}cke und ihre Abh{\"a}ngigkeit der verwendeten Methode. Die zwei unterschiedliche Materialklassen, welche untersucht wurden sind folgende: Erstens die organischen Systeme Cobalt-Phthalocyanin und Fulleren. An Ihnen wird der Einfluss der verwendeten Messmethoden aufgezeigt und die sich draus ergebenen HOMO- LUMO-L{\"u}cken (elektronisch, Volumen, Oberfl{\"a}che, optisch) diskutiert. Es zeigt sich, dass die optische Methode (Ellipsometrie) generell den kleinsten Wert und die elektronischen Methoden (XPS, XAS) den gr{\"o}ßten Wert ergeben. Die Gr{\"u}nde daf{\"u}r werden ausf{\"u}hrlich diskutiert. Durch die Kombination von XPS- , XAS- und Ellipsometrie-Messungen war es m{\"o}glich die Orientierung der aufgedampften CoPc-Molek{\"u}le auf den SiO2-Substrat zu bestimmen. Zweitens wurden die Metalloxide HfO2, Al2O3, In2O3 und Ga2O3 aufgrund ihrer großen technologischen Bedeutung untersucht. Mit Hilfe von ALD Zyklus-f{\"u}r-Zyklus Experimenten konnten die elektronischen Eigenschaften von HfO2 in Abh{\"a}ngigkeit der ALD- Zyklenzahl und das Wachstum von HfO2 in den ersten Zyklen studiert werden. Auf Basis der XPS- und EELS-Ergebnisse wurde ein Wachstumsmodell entwickelt. Es wird ebenfalls der Einfluss einer Dipolschicht an der Grenzfläche HfO2/SiO2 auf die Gr{\"o}ße der Bandl{\"u}cke in den EELS-Messungen diskutiert. Mittels resonanten Photoemission wurde ein neuer Auger-Mechanismus (3-Loch-Auger-Prozess) in den Oxiden gefunden. Dieser hat seine Ursache in Defekten. Defekte f{\"u}hren auch zu einer Fano-Anti-Resonanz, welche an der O1s-Absorptions-Kante beobachtet und diskutiert wird.}, language = {de} } @phdthesis{Richter, author = {Richter, Matthias}, title = {Excitons and Polarons in resonant Auger decay processes}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus-29816}, pages = {169}, abstract = {In the framework of this thesis synchrotron radiation spectroscopy is applied to study the electronic structure of organic semiconductors, of Graphene, and of transition metal (TM) oxide water splitting catalysts (Co-PI) with emphasis on excitonic and polaronic effects. For a correct theoretical description of the electronic structure of these material classes electron-phonon and electron-electron coupling as well as polarization and excitonic effects have to be considered. Excitons and Polarons are localized in-gap states. They are known to affect the optical properties of the material. Their influence can also be revealed in the resonant Auger decay profile. Even in TM-oxides Polarons and Excitons are observed as a consequence of an oxygen 2p to TM3d charge transfer. Therefor, the following three material classes are chosen for the fundamental study of Excitons and Polarons in resonant Auger decay processes. First, the existence of localized polaronic and excitonic states is investigated for regioregular-Poly(3 hexylthiophene-2,5-diyl) (rr-P3HT) and Phenyl-C61-butyric acid methyl ester (PCBM) used as a light absorber in organic solar cells. The existence of 2D-Polarons, singlet Exciton, and triplet Exciton is demonstrated for rr-P3HT whereas for PCBM only singlet Excitons are observed. Singlet Excitons show an influence on the resonant Auger decay by a combined spectator-participator (S+P) Auger decay in the π*-band. Second, for a more detailed study of the (S+P) decay Highly Ordered Pyrolytic Graphite (HOPG) is chosen. For Graphene as a single layer of HOPG without van der Waals force another combination of Auger decays can be observed: a double spectator Auger (S+S) and a double spectator Auger-Gain (S+S)* decay. Third, Co-PI (cobalt oxide compound) is investigated. It is a TM-oxide catalyst used for the oxygen evolution reaction in photo-electrochemical cells. Self-trapped Excitons formed by resonant core electron excitation into self-trapped hole states give rise to a combined Auger decay process (S+P). For all three novel Auger decay processes {(S+P), (S+S), and (S+S)*} a model is proposed.}, language = {en} } @misc{HaeberleRichterGalazkaetal., author = {Haeberle, J{\"o}rg and Richter, Matthias and Galazka, Zbigniew and Janowitz, Christoph and Schmeißer, Dieter}, title = {Resonant Photoemission at the O1s threshold to characterize In2O3 single crystals}, series = {Thin Solid Films}, volume = {2014}, journal = {Thin Solid Films}, number = {555}, issn = {0040-6090}, doi = {10.1016/j.tsf.2013.03.036}, pages = {53 -- 56}, abstract = {We report on spectroscopic investigations on In2O3 single crystals. We focus on the detailed analysis of the O1s resonance profile by resonant photoelectron spectroscopy. We analyze the electronic structure and assign the O2p to build the valence band and both, O2p and In5s5p states to contribute to the conduction band (CB). We determine the partial density of states for the valence and CBs and find a strong hybridization of O2p and In5s states. This is deduced from constant final state spectra on the O-KLL-Auger over the O K-edge and In M4,5-edge and a comparison to the corresponding X-ray absorption spectroscopy data.We also identify several types of defects. A broad band of oxygen derived defects is identified that extends throughout the gap. These are attributed to small polarons which cause an anti-resonance in the valence states around the O1s threshold. In addition, a separate Auger decay at resonance indicates the existence of localized charge transfer states which involves localized In5s5p states.}, language = {en} }