TY - CHAP A1 - Richter, Matthias A1 - Städter, Matthias A1 - Paloumpa, Ioanna A1 - Schmeißer, Dieter T1 - Multiple Auger Decay at resonant photo-excitation in carbon thin films T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft N2 - We use resonant photoemission at the C1s edge to study the electronic structure of HOPG, graphene flakes and monolayer graphene. We find remarkable differences in the profile of the Auger decay channels, which we attribute to an additional multiple-Auger with a three-hole final state. A prerequisite for the appearance of this decay mechanism is the existence of localized excitonic states, which cause the appearance of the multiple Auger decay. Defects (pits, holes, steps and kinks) can act as localized excitonic states. We use those effects to identify the existence and the quantity of such defect states within the pi*-band regime in carbon thin films, because the intensity of the three-hole Auger decay is varying with the defect density of the carbon films. The defect-excitonic states can be either localized in the band-gap at the M-point or in case of surface defects like steps, kinks or pits even at the K-point by losing the pure sp2 character of the films. We find that the appearance of the multiple Auger decay is different for multilayer and monolayer graphene. In particular the interaction of impurities leads to broadening of the C1s core levels. The three-hole Auger decay spectroscopy is a new method to detect such contaminations with a high sensitivity. KW - resonant photoelectron spectroscopy KW - Auger decay KW - multiple decay KW - carbon thin films Y1 - 2013 UR - http://www.dpg-verhandlungen.de/year/2013/conference/regensburg/part/hl/session/52/contribution/6?lang=de PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Städter, Matthias A1 - Richter, Matthias A1 - Schmeißer, Dieter T1 - Fano-Profiles in HOPG and graphene flakes T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft N2 - We investigated the electronic structure of the valence and conduction band of HOPG by 2D resonant photoemission spectroscopy. Our aim is to understand the electronic structure of defects and inhomogeneities in graphene and related materials in more detail. From our measurements we find that the transition from the sigma-band to the pi*-band at the M-point shows a characteristic Fano-Profile. A Fano-Profile occurs as the result of the interference of the band to band transition and a parallel transition to a discrete energy level within the band gap. The theory of Fano enables us to determine the energetic location of these discrete level. It is found to be several meV above the Fermi-Energy. Additional measurements on graphene flakes lead to similar results for the sigma- to pi*-band transition and the location of the discrete energy state. With this we not only can determine the energetic states of defects but also get a better understanding of the origin of the Fano profile which is a particular detail of the resonant absorption process. KW - resonant photoelectron spectroscopy KW - Fano profiles KW - Graphene KW - HOPG Y1 - 2013 UR - http://www.dpg-verhandlungen.de/year/2013/conference/regensburg/part/hl/session/52/contribution/5?lang=de PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Fischer, Christian B. A1 - Rohrbeck, Magdalena A1 - Wehner, Stefan A1 - Richter, Matthias A1 - Städter, Matthias A1 - Schmeißer, Dieter T1 - Interlayer formation of Diamond-Like Carbon Coatings on Polyethylene Plastic Material T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft N2 - The coating of materials with diamond-like carbon (DLC) is a very common way to further improve and modify surface specific properties. Although DLC is frequently used as a protective coating on several substrates, the chemical and physical properties throughout the coating process on plastics are yet sparsely investigated. Different layer thicknesses of two types of protective coatings one sp3-enriched (robust, r-type) and one with more sp2-centers (flexible, f-type) have been realized on polyethylene by PECVD. Microscopic analysis showed diverse surface topographies for the two DLC-types. NEXAFS spectroscopy revealed significant details of carbon centers in chemically different neighborhood displaying a characteristic fingerprint behavior. The appropriate explanation for the current carbon deposition process is obviously the formation of an interlayer between these unequal materials. An improved understanding of hard DLC and soft polyethylene assembly is part of the present work. KW - Diamond-like carbon (DLC) KW - topography KW - X-ray absorption spectroscopy KW - plasma enhanced chemical vapor deposition Y1 - 2013 UR - http://www.dpg-verhandlungen.de/year/2013/conference/regensburg/part/o/session/33/contribution/4?lang=de PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - GEN A1 - Rudolph, Matthias A1 - Achouche, M. A1 - Kraus, S. A1 - Spitzbart, Th. A1 - Kurpas, Paul A1 - Rentner, D. A1 - Brunner, F. A1 - Richter, E. A1 - Bergunde, T. A1 - Heymann, Peter A1 - Wolter, P. A1 - Wittrich, H. A1 - Weyers, M. A1 - Würfl, Joachim A1 - Tränkle, Günther T1 - InGaP/GaAs Power HBTs for L-Band Applications Y1 - 1999 ER - TY - CHAP A1 - Rudolph, Matthias A1 - Dörner, Ralf A1 - Heymann, Peter A1 - Richter, E. T1 - Scaling of GaInP/GaAs HBT Equivalent-Circuit Elements Y1 - 1999 ER - TY - GEN A1 - Friedrich, Daniel A1 - Henkel, Karsten A1 - Richter, Matthias A1 - Schmeißer, Dieter T1 - Fullerenol as probed by Synchrotron X-Ray Photoemission and Absorption Spectroscopy Y1 - 2011 ER - TY - GEN A1 - Müller, Klaus A1 - Richter, Matthias A1 - Philip, Shine A1 - Kunst, Manuel A1 - Schmeißer, Dieter T1 - Excited states in P3HT and P3HT/PCBM blends T2 - BioNanoScience Y1 - 2012 SN - 2191-1630 VL - 2 IS - 1 SP - 42 EP - 51 ER - TY - GEN A1 - Richter, Matthias A1 - Friedrich, Daniel A1 - Schmeißer, Dieter T1 - Valence and Conduction band states of PCBM as probed by photoelectron spectroscopy at resonant excitation T2 - BioNanoScience Y1 - 2012 SN - 2191-1630 VL - 2 IS - 1 SP - 59 EP - 65 ER - TY - CHAP A1 - Osterrieder, Peter A1 - Richter, Stefan A1 - Friedrich, Matthias T1 - Lateral buckling of continuous steel beams with hinges Y1 - 2010 ER - TY - GEN A1 - Müller, Klaus A1 - Richter, Matthias A1 - Friedrich, Daniel A1 - Paloumpa, Ioanna A1 - Kramm, Ulrike Ingrid A1 - Schmeißer, Dieter T1 - Spectroscopic characterization of Cobalt–Phthalocyanine electrocatalysts for fuel cell applications T2 - Solid State Ionics N2 - For polymer–electrolyte–membrane fuel cells (PEM-FC), platinumcatalysts on carbon based substrates are state of the art, due to high electrochemical activity and chemical stability in acid electrolytes. High costs of platinum force investigations of alternative catalysts. With respect to the oxygen reduction reaction, possible candidates are transition metal (TM) complexes like TM-porphyrines or TM-phthalocyanines. Pyrolysis on carbon based substrates improves the catalytic activity. Highest activities were found for Fe or Co as transition metal centers. We present results of the pyrolysis of Co-phthalocyanine (CoPc) on carbon black. Besides an investigation of morphology by scanning electron microscopy (SEM) and chemical composition by energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) during pyrolysis, we present a near edge X-ray absorption fine structure (NEXAFS) study of the chemical composition for the related annealing steps. This investigation is accompanied by an electrochemical characterization of the catalytic activity and selectivity. The XPS and NEXAFS data indicate a decomposition of the CoN4(chelate-) complex during pyrolysis. The N1s data for 800 °C show graphite-like, formally pyrrolic and pyridinic like features, without any significant contri-bution of Co. The Co2p data for both, XPS and NEXAFS are dominated by CoO/Co2O3. It can be concluded that during the pyrolysis cobalt particles are formed by the disintegration of CoN4-centers, after pyrolysis these par-ticles become oxidized upon contact with air. KW - Co-phthalocyanine KW - Catalysis KW - Oxygen reduction reaction (ORR) KW - XPS KW - NEXAFS Y1 - 2012 U6 - https://doi.org/10.1016/j.ssi.2011.12.013 SN - 1872-7689 IS - 216 SP - 78 EP - 82 ER - TY - GEN A1 - Fischer, Christian B. A1 - Rohrbeck, Magdalena A1 - Wehner, Stefan A1 - Richter, Matthias A1 - Schmeißer, Dieter T1 - Interlayer formation of diamond-like carbon coatings on industrial polyethylene: Thickness dependent surface characterization by SEM, AFM and NEXAFS T2 - Applied Surface Science N2 - The coating of materials with diamond-like carbon (DLC) is a very common way to change and improve their basic characteristics. Although DLC is used on several substrates, the chemical and physical properties throughout the coating process on plastics are yet sparsely investigated. Two types of protective coatings one sp3-enriched (robust, r-type) and one with more sp2-centers (flexible, f-type) have been realized on polyethylene by PECVD deposition. SEM and AFM analysis of coated samples of DLC types revealed diverse surface topographies on different scales and images appeared even differently smoothed by the carbonaceous deposits. Grains of both DLC types are platelet-shaped and nearly double in size for the robust type indicating fundamental differences in the epitaxial DLC growth. NEXAFS spectroscopy showed significant details of carbon centers in chemically different neighborhood displaying a characteristic fingerprint behavior. Comparison of deposition models revealed a mechanism of interlayer formation which is discussed in detail. Interlayer formation is clearly the appropriate explanation of the process for the current carbon deposition between these two unequal materials. An improved understanding of hard DLC and soft polyethylene assembly is given in the presented work. KW - Diamond-like carbon KW - Interlayer formation KW - Polyethylene KW - Surface characterization KW - Coatings KW - Plastics Y1 - 2013 U6 - https://doi.org/10.1016/j.apsusc.2013.01.210 SN - 0169-4332 IS - 271 SP - 381 EP - 389 ER - TY - GEN A1 - Richter, Matthias A1 - Paloumpa, Ioanna A1 - Friedrich, Daniel A1 - Schmeißer, Dieter T1 - Multiple Auger Decay At Resonant Photo-Excitation In Carbon Thin Films T2 - ECS Transactions N2 - We use resonant photoemission at the C1s edge to study the electronic structure of HOPG, graphene flakes and monolayer graphene. We find remarkable differences in the profile of the Auger decay channels, which we attribute to an additional multiple-Auger with a three-hole final state. A prerequisite for the appearance of this decay mechanism is the existence of localized excitonic states, which cause the appearance of the multiple Auger decay. We use those effects to identify the existence and the quantity of such defect states within the π*-band regime in carbon thin films, because the intensity of the three-hole Auger decay is varying with the defect density of the carbon films. We find that the appearance of the multiple Auger decay is different for multilayer and monolayer graphene. In particular the interaction of impurities leads to broadening of the C1s core levels. The three-hole Auger decay spectroscopy is a new method to detect such contaminations with a high sensitivity. KW - resonant photoelectron spectroscopy KW - graphene KW - HOPG KW - X-ray absorption spectroscopy (XAS) KW - X-ray photoelectron spectroscopy (XPS) Y1 - 2013 U6 - https://doi.org/10.1149/05020.0009ecst VL - 50 IS - 20 SP - 9 EP - 21 ER -