@article{LopezBitzerHelleretal., author = {Lopez, A. and Bitzer, Thomas and Heller, Thomas and Richardson, Neville V.}, title = {Adsorption of water on alkoxy modified Si(1 0 0), Si(1 1 3) and Si(1 1 5) surfaces}, language = {en} } @article{LopezHellerBitzeretal., author = {Lopez, A. and Heller, Thomas and Bitzer, Thomas and Chen, Q. and Richardson, Neville V.}, title = {The influence of sodium on the adsorption of water on SrTiO3(100)-1x1 surfaces}, language = {en} } @inproceedings{HellerLopezBitzeretal., author = {Heller, Thomas and Lopez, Alberto and Bitzer, Thomas and Richardson, Neville V. and Schmeißer, Dieter}, title = {The Adsorption of Maleic Anhydride on Si(100)-2x1: A Combined HREELS and NEXAFS Study}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {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.}, language = {en} } @inproceedings{HellerLopezBitzeretal., author = {Heller, Thomas and Lopez, Alberto and Bitzer, Thomas and Richardson, Neville V. and Schmeißer, Dieter}, title = {Isopropoxy induced stabilisation of the 2x1 reconstruction of Si(100)}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {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.}, language = {en} } @article{LopezBitzerHelleretal., author = {Lopez, A. and Bitzer, Thomas and Heller, Thomas and Richardson, Neville V.}, title = {Functional group selectivity in adsorption of 4-aminobenzoic acid on clean and Na modified Si(100)-2 x 1 surfaces}, language = {en} } @article{BitzerLopezHelleretal., author = {Bitzer, Thomas and Lopez, A. and Heller, Thomas and Richardson, Neville V.}, title = {The Adsorption of maleic anhydride on Si(100)-2x1: A combined HREELS and NEXAFS study}, language = {en} } @misc{LopezHellerBitzeretal., author = {Lopez, Alberto and Heller, Thomas and Bitzer, Thomas and Richardson, Neville V.}, title = {A vibrational study of the adsorption of glycine on clean and Na modified Si (100)-2x1 surfaces}, series = {Chemical physics}, volume = {277}, journal = {Chemical physics}, number = {1}, issn = {0301-0104}, pages = {1 -- 8}, abstract = {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.}, language = {en} } @article{LopezBitzerHelleretal., author = {Lopez, A. and Bitzer, Thomas and Heller, Thomas and Richardson, Neville V.}, title = {Adsorption of maleic anhydride on Si(1 0 0)-2 x 1}, series = {Surface Science}, volume = {477}, journal = {Surface Science}, issn = {0039-6028}, pages = {219 -- 226}, language = {en} } @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} } @inproceedings{HellerBoehmeSchmeisser, author = {Heller, Thomas and B{\"o}hme, Oliver and Schmeißer, Dieter}, title = {Gap - Zust{\"a}nde in Wolframoxid WO3 - relaxierten Oberfl{\"a}chen}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {Vorgestellt werden Arbeiten an d{\"u}nnen WO3-Schichten, die durch Verdampfen aus einer Knudsenzelle im UHV pr{\"a}pariert wurden. Diese Filme sind im Rahmen der XPS-Analysen st{\"o}chiometrisch, ohne Gap-Zust{\"a}nde. Definierte Gap-Zust{\"a}nde bilden sich durch Relaxierung der Oberfl{\"a}che: nach einigen Stunden im UHV, nach Heizen in Argon-Atmosph{\"a}re und nach Belegung mit Natrium. Die Charakterisierung dieser definierten Wolframoxid-Schichten erfolgt durch: 1.)XPS-Intensit{\"a}ten 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-Zust{\"a}nden in der Bandl{\"u}cke}, language = {de} } @misc{HirschRaabHelleretal., author = {Hirsch, Florian and Raab, Thomas and Heller, Sebastian and Bauriegel, Albrecht}, title = {Classification of pedogenic cementation in Podzols by pocket penetrometry}, series = {Journal of Plant Nutrition and Soil Science}, volume = {180}, journal = {Journal of Plant Nutrition and Soil Science}, number = {4}, issn = {1522-2624}, doi = {10.1002/jpln.201600395}, pages = {430 -- 435}, abstract = {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.}, language = {en} } @inproceedings{HellerSchmeisser, author = {Heller, Thomas and Schmeißer, Dieter}, title = {Polaronen in SrTiO3(100)}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {Vorgestellt werden Untersuchungen zur elektronischen Struktur von oxidischen Halbleitern wie SrTiO3(100)-Einkristallen und WO3-Filmen. Die Charakterisierung der Oberfl{\"a}chen erfolgt im Valenzbandbereich mittels Photoelektronenspektroskopie (TGM 7, Bessy I, hν=3D 15-100eV). Zust{\"a}nde entstehen in der Bandl{\"u}cke dieser=20 Materialien durch Dotierung (Heizen oder Natrium-Belegung). Wir untersuchen den Wirkungsquerschnitt speziell f{\"u}r diese Gapzust{\"a}nde. Ohne Dotierung ist der Verlauf des Wirkungsquerschnittes unstrukturiert. Bei Dotierung bilden sich molekulare Resonanzen. Deren Auftreten zeigt, daß diese Gapzust{\"a}nde lokalisiert sind. Weiterhin beobachten wir ausgepr{\"a}gte Feinstrukturen, die die charakteristische Anregung f=FCr Polaronen enthalten.}, language = {de} } @inproceedings{HellerBoehmeSchmeisser, author = {Heller, Thomas and B{\"o}hme, Oliver and Schmeißer, Dieter}, title = {Molecular Resonances in the Photoionization Cross Section (PIX) of Oxidic Semiconductors}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {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.}, language = {en} } @article{SieberMantelSeylleretal., author = {Sieber, N. and Mantel, B. F. and Seyller, Th. and Ristein, J. and Ley, L. and Heller, Thomas and Batchelor, David R. and Schmeißer, Dieter}, title = {Structural, electronic and chemical properties of hydrogen terminated 6H-SiC}, language = {en} } @article{HellerBoehmeTontietal., author = {Heller, Thomas and B{\"o}hme, O. and Tonti, D. and Klein, A. and Jaegermann, Wolfram and Schmeißer, Dieter}, title = {Na interaction with relaxed WO3 thin films}, language = {en} } @article{SieberMantelSeylleretal., author = {Sieber, N. and Mantel, B. F. and Seyller, Th. and Ristein, J. and Ley, L. and Heller, Thomas and Batchelor, David R. and Schmeißer, Dieter}, title = {Electronic and chemical passivation of hexagonal 6H-SiC surfaces by hydrogen termination}, language = {en} } @article{SchmeisserAppelBoehmeetal., author = {Schmeißer, Dieter and Appel, G{\"u}nter and B{\"o}hme, O. and Heller, Thomas and Mikalo, Ricardo Pablo and Hoffmann, Patrick and Batchelor, David R.}, title = {Nanoparticles and polarons: active centers in thin film sensor devices}, language = {de} } @article{MikaloHoffmannHelleretal., author = {Mikalo, Ricardo Pablo and Hoffmann, Patrick and Heller, Thomas and Batchelor, David R. and Appel, G{\"u}nter and Schmeißer, Dieter}, title = {Doping and defect inhomogeneities of polypyrrole tosylate films as revealed by ?-NEXAFS}, language = {en} } @article{MikaloHoffmannHelleretal., author = {Mikalo, Ricardo Pablo and Hoffmann, Patrick and Heller, Thomas and Schmeißer, Dieter}, title = {Lateral Doping Inhomogeneities as Revealed by ?-NEXAFS and ?-PES}, language = {en} } @article{HellerBoehmeSchmeisser, author = {Heller, Thomas and B{\"o}hme, O. and Schmeißer, Dieter}, title = {Polarons in oxidic semiconductors - the SrTiO3 case}, language = {en} }