TY - JOUR A1 - Lopez, A. A1 - Bitzer, Thomas A1 - Heller, Thomas A1 - Richardson, Neville V. T1 - Adsorption of water on alkoxy modified Si(1 0 0), Si(1 1 3) and Si(1 1 5) surfaces Y1 - 2001 ER - TY - JOUR A1 - Lopez, A. A1 - Heller, Thomas A1 - Bitzer, Thomas A1 - Chen, Q. A1 - Richardson, Neville V. T1 - The influence of sodium on the adsorption of water on SrTiO3(100)-1x1 surfaces Y1 - 2001 ER - TY - CHAP A1 - Heller, Thomas A1 - Lopez, Alberto A1 - Bitzer, Thomas A1 - Richardson, Neville V. A1 - Schmeißer, Dieter T1 - The Adsorption of Maleic Anhydride on Si(100)-2x1: A Combined HREELS and NEXAFS Study T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft N2 - Due to the growing range of applications for organic materials considerable interest has been focused on the controlled growth of films on silicon substrates. Recently, it has been shown that ultra-thin oligimide films can be grown on Si(100)-2x1 with a direct Si-C linkage to the substrate. In this study, we have focused on the chemisorption of maleic anhydride (C4O3H2) on Si(100)-2x1. The combined HREELS data indicate that the adsorption of maleic anhydride on Si(100)-2x1 at low dosages occurs mainly through cycloaddition of the C=C bond to the dangling bonds of the Si-Si dimer analogous to the behaviour of ethene. The Si-Si dimer bonds are not involved in the chemisorption, as the continued observation of a 2x1 pattern in LEED shows. In the NEXAFS spectra, a π* resonance indicative of a C=C bond is absent upon exposure of the silicon substrate to maleic anhydride. At higher dosages, we observe chemisorbed maleic anhydride species, which are bonded to the Si surface atoms via a single Si-C linkage with preservation of the C=C double bond. In this case, the dissociated hydrogen bonds to one of the neighbouring Si atoms. Possible adsorption geometries will be discussed. KW - adsorption KW - maleic anhydride KW - High resolution electron energy loss spectroscopy (HREELS) KW - low-energy electron diffraction (LEED) KW - Near-edge X-Ray absorption spectroscopy (NEXAFS) Y1 - 2000 UR - http://www.dpg-verhandlungen.de/year/2000/conference/regensburg/part/o/session/11/contribution/56?lang=en PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Heller, Thomas A1 - Lopez, Alberto A1 - Bitzer, Thomas A1 - Richardson, Neville V. A1 - Schmeißer, Dieter T1 - Isopropoxy induced stabilisation of the 2x1 reconstruction of Si(100) T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft N2 - Alcohols are successfully employed as an additive in the anisotropic etching of silicon. In this HREELS study, we modelled the silicon/etching interface by the adsorption of alcohols (ethanol, isopropanol, n-propanol, tert-butyl alcohol) on Si(100)-2x1 and post-exposure to H2O under ultra high vacuum conditions. The vibrational data show that the adsorption of the alcohol molecules involves the cleavage of the O-H bond and the formation of a Si-O-C linkage to the alkoxy species. The dissociated hydrogen saturates one of the neighbouring dangling Si bonds. The Si-Si dimer bonds are not involved in the adsorption process. We observe a considerable chemisorption of water on the ethoxy and tert-butoxy passivated Si(100)-2x1 surface. From the disappearance of the 2x1 LEED pattern it can be concluded that the chemisorption of water occurs through a cleavage of the Si-Si dimer bond. In contrast, isopropoxy species on Si(100)-2x1 reduces dramatically the reactivity of Si(100)-2x1 towards water. Even following extreme exposures to water (1012 Torr s), a 2x1 LEED pattern was observed indicating the presence of intact Si-Si dimer bonds at the isopropoxy/Si(100)-2x1 surface. KW - alcohol adsorption KW - anisotropic etching KW - high resolution electron energy loss spectroscopy (HREELS) KW - low-energy electron diffraction (LEED) Y1 - 2000 UR - http://www.dpg-verhandlungen.de/year/2000/conference/regensburg/part/o/session/11/contribution/55?lang=en PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - JOUR A1 - Lopez, A. A1 - Bitzer, Thomas A1 - Heller, Thomas A1 - Richardson, Neville V. T1 - Functional group selectivity in adsorption of 4-aminobenzoic acid on clean and Na modified Si(100)-2 x 1 surfaces Y1 - 2001 ER - TY - JOUR A1 - Bitzer, Thomas A1 - Lopez, A. A1 - Heller, Thomas A1 - Richardson, Neville V. T1 - The Adsorption of maleic anhydride on Si(100)-2x1: A combined HREELS and NEXAFS study Y1 - 2000 ER - TY - GEN A1 - Lopez, Alberto A1 - Heller, Thomas A1 - Bitzer, Thomas A1 - Richardson, Neville V. T1 - A vibrational study of the adsorption of glycine on clean and Na modified Si (100)-2x1 surfaces T2 - Chemical physics N2 - The chemisorption of glycine and its fully deuterated analogue, d(5)-glycine, deposited on the clean and Na modified Si(100)-2 x 1 surfaces, has been studied byhigh-resolution electron energy loss spectroscopy (HREELS) and ab initio methods. HREELS indicates that chemisorption of glycine and d(5)-glycine on Na/Si(100)-2 x1 occurs through cleavage of the OH and OD bonds in the carboxylic groups. The adsorbed species are bonded through the formation of an ionic bond between thedeprotonated carboxylate group and the adsorbed Na atom, leading to species in a bidentate coordination. In contrast, we observe monodentate glycinate andd(5)-glycinate species following the exposure of Si(100)-2 x 1 to glycine and deuterated glycine. The thermal stability of glycine on clean Si(100)-2 x 1 and on the Namodified surface has been studied by heating the substrate to various temperatures. KW - Silicon KW - Glycine KW - Sodium KW - Ab initio KW - HREELS Y1 - 2002 SN - 0301-0104 VL - 277 IS - 1 SP - 1 EP - 8 ER - TY - JOUR A1 - Lopez, A. A1 - Bitzer, Thomas A1 - Heller, Thomas A1 - Richardson, Neville V. T1 - Adsorption of maleic anhydride on Si(1 0 0)-2 x 1 JF - Surface Science Y1 - 2001 SN - 0039-6028 VL - 477 SP - 219 EP - 226 ER - TY - THES A1 - Heller, Thomas T1 - Molekulare Resonanzen im Wirkungsquerschnitt der Photoemission in den Valenzzuständen der stöchiometrischen und der mit Natrium belegten WO3 und TiO2 (110) 1x1 Oberfläche KW - WO3 KW - TiO2 KW - Photoelektronenspektroskopie KW - Natriumadsorption Y1 - 2002 SN - 3-8322-0742-2 PB - Shaker CY - Aachen ER - TY - CHAP A1 - Heller, Thomas A1 - Böhme, Oliver A1 - Schmeißer, Dieter T1 - Gap - Zustände in Wolframoxid WO3 - relaxierten Oberflächen T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft N2 - Vorgestellt werden Arbeiten an dünnen WO3-Schichten, die durch Verdampfen aus einer Knudsenzelle im UHV präpariert wurden. Diese Filme sind im Rahmen der XPS-Analysen stöchiometrisch, ohne Gap-Zustände. Definierte Gap-Zustände bilden sich durch Relaxierung der Oberfläche: nach einigen Stunden im UHV, nach Heizen in Argon-Atmosphäre und nach Belegung mit Natrium. Die Charakterisierung dieser definierten Wolframoxid-Schichten erfolgt durch: 1.)XPS-Intensitäten 2.)detailierte Analyse der W4f-Rumpfniveaus durch Synchrotronstrahlung (Bessy, TGM 7) 3.)die Variation der Austrittsarbeit beim Heizen und bei Natrium-Belegung 4.)das Auftreten von Gap-Zuständen in der Bandlücke KW - WO3 KW - Röntgen-Photoelektronenspektroskopie (XPS) KW - Gapzustände Y1 - 1998 UR - http://www.dpg-verhandlungen.de/year/1998/conference/regensburg/part/o/session/11/contribution/102?lang=en PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - GEN A1 - Hirsch, Florian A1 - Raab, Thomas A1 - Heller, Sebastian A1 - Bauriegel, Albrecht T1 - Classification of pedogenic cementation in Podzols by pocket penetrometry T2 - Journal of Plant Nutrition and Soil Science N2 - According to the German Soil Taxonomy, the formation of cemented horizons in Podzols is restricted to the precipitation of iron oxides. However, in iron-poor sandy substrates, also illuviation of only organic compounds can form cemented horizons with penetration resistances of up to 14 kg cm−2. We present a reproducible field test for classifying pedogenic cementation in Podzols and suggest considering cemented horizons (Bmh and Bhm) in the upcoming edition of the Guidelines for Soil Mapping. KW - field techniques KW - micromorphology KW - soil classification KW - soil development KW - soil systematics Y1 - 2017 UR - http://onlinelibrary.wiley.com/doi/10.1002/jpln.201600395/abstract U6 - https://doi.org/10.1002/jpln.201600395 SN - 1522-2624 VL - 180 IS - 4 SP - 430 EP - 435 ER - TY - CHAP A1 - Heller, Thomas A1 - Schmeißer, Dieter T1 - Polaronen in SrTiO3(100) T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft N2 - Vorgestellt werden Untersuchungen zur elektronischen Struktur von oxidischen Halbleitern wie SrTiO3(100)-Einkristallen und WO3-Filmen. Die Charakterisierung der Oberflächen erfolgt im Valenzbandbereich mittels Photoelektronenspektroskopie (TGM 7, Bessy I, hν=3D 15-100eV). Zustände entstehen in der Bandlücke dieser=20 Materialien durch Dotierung (Heizen oder Natrium-Belegung). Wir untersuchen den Wirkungsquerschnitt speziell für diese Gapzustände. Ohne Dotierung ist der Verlauf des Wirkungsquerschnittes unstrukturiert. Bei Dotierung bilden sich molekulare Resonanzen. Deren Auftreten zeigt, daß diese Gapzustände lokalisiert sind. Weiterhin beobachten wir ausgeprägte Feinstrukturen, die die charakteristische Anregung f=FCr Polaronen enthalten. KW - Polaron KW - Röntgen-Photoelektronenspektroskopie KW - Gapzustände Y1 - 1999 UR - http://www.dpg-verhandlungen.de/year/1999/conference/muenster/part/o/session/21/contribution/8?lang=en PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Heller, Thomas A1 - Böhme, Oliver A1 - Schmeißer, Dieter T1 - Molecular Resonances in the Photoionization Cross Section (PIX) of Oxidic Semiconductors T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft N2 - Despite their fascinating physical applications in sensoric there is no clear view of the electronic structure of these class of oxidic semiconductor materials. We studied the photo ionization cross sections (PIX) in a CIS like experiment of the valence states as well as the defect state and compare these to the CFS data obtained from X-ray absorption spectroscopy. While the first technique contains only transitions from a defined initial state the latter covers all the possible optical channels. We show for WO3-films that a structural reorganization of the surface is induced by doping (Na exposure) which increases the O2p/W5d orbital mixing. Pristine TiO2 (110) single crystals show basically the same behavior but have an initially stronger hybridization of Ti3d derived states with the O2p valence states. Upon doping the defect intensity is increased as well as the orbital hybridization. Our data give evidence that valence band derived states have almost the same orbital parentage like the defect state. They offer that the wave functions of these states are localized on a molecular scale. This is in contrast to the common treatment of resonances in the PIX which are usually discussed in terms of the resonant photoemission model, which does not include the possibility of mixed valence/defect states. KW - X-Ray photoelectron spectroscopy KW - X-Ray absorption spectroscopy KW - Photoionization Cross Section (PIX) KW - defect states Y1 - 2000 UR - http://www.dpg-verhandlungen.de/year/2000/conference/regensburg/part/o/session/15/contribution/3?lang=en PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - JOUR A1 - Sieber, N. A1 - Mantel, B. F. A1 - Seyller, Th. A1 - Ristein, J. A1 - Ley, L. A1 - Heller, Thomas A1 - Batchelor, David R. A1 - Schmeißer, Dieter T1 - Structural, electronic and chemical properties of hydrogen terminated 6H-SiC Y1 - 2001 ER - TY - JOUR A1 - Heller, Thomas A1 - Böhme, O. A1 - Tonti, D. A1 - Klein, A. A1 - Jaegermann, Wolfram A1 - Schmeißer, Dieter T1 - Na interaction with relaxed WO3 thin films Y1 - 1998 ER - TY - JOUR A1 - Sieber, N. A1 - Mantel, B. F. A1 - Seyller, Th. A1 - Ristein, J. A1 - Ley, L. A1 - Heller, Thomas A1 - Batchelor, David R. A1 - Schmeißer, Dieter T1 - Electronic and chemical passivation of hexagonal 6H-SiC surfaces by hydrogen termination Y1 - 2001 ER - TY - JOUR A1 - Schmeißer, Dieter A1 - Appel, Günter A1 - Böhme, O. A1 - Heller, Thomas A1 - Mikalo, Ricardo Pablo A1 - Hoffmann, Patrick A1 - Batchelor, David R. T1 - Nanoparticles and polarons: active centers in thin film sensor devices Y1 - 2000 ER - TY - JOUR A1 - Mikalo, Ricardo Pablo A1 - Hoffmann, Patrick A1 - Heller, Thomas A1 - Batchelor, David R. A1 - Appel, Günter A1 - Schmeißer, Dieter T1 - Doping and defect inhomogeneities of polypyrrole tosylate films as revealed by ?-NEXAFS Y1 - 1999 ER - TY - JOUR A1 - Mikalo, Ricardo Pablo A1 - Hoffmann, Patrick A1 - Heller, Thomas A1 - Schmeißer, Dieter T1 - Lateral Doping Inhomogeneities as Revealed by ?-NEXAFS and ?-PES Y1 - 1998 ER - TY - JOUR A1 - Heller, Thomas A1 - Böhme, O. A1 - Schmeißer, Dieter T1 - Polarons in oxidic semiconductors - the SrTiO3 case Y1 - 1999 ER - TY - JOUR A1 - Schmeißer, Dieter A1 - Böhme, O. A1 - Yfantis, Alexandros D. A1 - Heller, Thomas A1 - Batchelor, David R. A1 - Lundström, Ingemar A1 - Lloyd Spetz, Anita T1 - Dipole moment of nanoparticles at interfaces Y1 - 1999 ER -