@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} } @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} } @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{HoffmannMikaloSchmeisseretal., author = {Hoffmann, Patrick and Mikalo, Ricardo Pablo and Schmeißer, Dieter and Kittler, Martin}, title = {Spektro-Mikroskopie auf multikristallinem Silizium}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {Es werden spektro-mikroskopische Untersuchungen an multikristallinem Silizium (mc-Si) vorgestellt, einem aussichtsreichen Material f{\"u}r die Herstellung preiswerter Solarzellen. Dazu wird ein Photoemissions- Elektronenmikroskop (PEEM) ausgestattet mit einem zus{\"a}tzlichen Energieanalysator f{\"u}r Elektronen (µESCA) genutzt. Bei Verwendung eines Synchrotrons als Anregungsquelle ist es so m{\"o}glich, sowohl Absorbtions-Spektren (NEXAFS) als auch Photoelektronen-Spektren (PES) mit Ortsaufl{\"o}sung zu erhalten. Dabei wird gezeigt, dass das nat{\"u}rliche Oxid zur Untersuchung der morphologie-abh{\"a}ngigen Oberfl{\"a}chenpotentiale nicht entfernt werden muss. Des Weiteren wird die Verteilung von Ca- und Na-Ausscheidungen, die auf dem mc-Si gefunden wurden, durch ortsaufgel{\"o}stes NEXAFS bzw. PES dargestellt. F{\"u}r den Photoemissions-Prozess des mc-Si im PEEM wird ein Modell aufgestellt, welches Photoemission mit einer Quecksilberdampflampe (hνmax = 4,9 eV) erkl{\"a}rt.}, language = {de} } @inproceedings{MikaloAppelHoffmannetal., author = {Mikalo, Ricardo Pablo and Appel, G{\"u}nter and Hoffmann, Patrick and Schmeißer, Dieter}, title = {Conducting Polypyrrole doped with Phthalocyaninesulfonates - new materials for chemical sensors}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {Polypyrrole - a conducting polymer - is used as an active electrode of a quartz micro ballance and considered as a gate electrode in all-polymer field effect transistors used as chemical sensor. We use substituted phthalocyanines as dopants of polypyrrole as they offer the possibility to enhance the dopant concentration as well as to include functionalized groups. We studied these films by photoelectron spectroscopy, NEXAFS, PEEM, and TEM. These investigations revealed that the electronic structure as well as the morphology are highly dependent on the dopant's structure. We suggest a new charge transport model for 5-ring heterocycle conductive polymers. Whereas in the standard model only the carbon backbone is considered for the charge transport, we found by NEXAFS investigations that the heteroatom has a considerable high participation in the gap states, which are responsible for the charge transport. The dopants π-interactions force the nitrogen lone pair wave functions to contribute to the conducting polymer π-system. This is a novel approach concerning the application as chemical sensors since the reversible interaction of the analyte modifies the dopant and not the matrix.}, 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} } @article{MikaloAppelHoffmannetal., author = {Mikalo, Ricardo Pablo and Appel, G{\"u}nter and Hoffmann, Patrick and Schmeißer, Dieter}, title = {Determination of the Vacuum Level in NEXAFS-spectra by Selected-Yield-NEXAFS}, language = {en} } @misc{BatchelorSchmeisserFollath, author = {Batchelor, David R. and Schmeißer, Dieter and Follath, Rolf}, title = {The BTU Cottbus Beamline at BESSY II}, language = {de} } @article{HoffmannMikaloSchmeisser, author = {Hoffmann, Patrick and Mikalo, Ricardo Pablo and Schmeißer, Dieter}, title = {Photoemissionselektronenmikroskopie - ein Instrument f{\"u}r die Materialforschung}, language = {de} } @article{AppelBoehmeMikaloetal., author = {Appel, G{\"u}nter and B{\"o}hme, O. and Mikalo, Ricardo Pablo and Schmeißer, Dieter}, title = {The polaron and bipolaron contributions to the electronic structure of polypyrrole films}, language = {en} } @article{SchmeisserBoehmeYfantisetal., author = {Schmeißer, Dieter and B{\"o}hme, O. and Yfantis, Alexandros D. and Heller, Thomas and Batchelor, David R. and Lundstr{\"o}m, Ingemar and Lloyd Spetz, Anita}, title = {Dipole moment of nanoparticles at interfaces}, language = {de} } @article{HoffmannMikaloSchmeisseretal., author = {Hoffmann, Patrick and Mikalo, Ricardo Pablo and Schmeißer, Dieter and Kittler, Martin}, title = {A spectro-microscopic approach to study the morphology and elemental distribution of mc-Si surfaces}, language = {en} } @article{OpreaHenkelOehmgenetal., author = {Oprea, A. and Henkel, Karsten and Oehmgen, R. and Appel, G{\"u}nter and Schmeißer, Dieter and Lauer, H. and Hausmann, P.}, title = {Increased sensor sensitivities obtained by polymer coated quartz microbalances}, language = {en} } @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{YfantisAppelSchmeisseretal., author = {Yfantis, Alexandros D. and Appel, G{\"u}nter and Schmeißer, Dieter and Yfantis, Alexandros D.}, title = {Polypyrrole doped with fluoro-metal complexes: thermal stability and structural properties}, language = {en} } @article{AppelSchmeisserBaueretal., author = {Appel, G{\"u}nter and Schmeißer, Dieter and Bauer, Jakob and Bauer, Monika and Egelhaaf, H. J. and Oelkrug, D.}, title = {The formation of oligomers in the electrolyte upon polymerization of pyrrole}, 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} } @inproceedings{BatchelorFollathSchmeisser, author = {Batchelor, David R. and Follath, Rolf and Schmeißer, Dieter}, title = {Design of a PGM for the U49/2 Undulator at BESSY II}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {This poster describes the beamline proposed for the BESSY II U49/2 Undulator by the Collaborating Research Group of BTU Cottbus, HMI Berlin and the TU Darmstadt. The beamline is designed with both high resolution electron spectroscopy, valence band measurements and PEEM in mind and utilises the wide energy range of the U49 Undulator 40-1500eV. The design chosen is based on a Petersen PGM [1] but with the grating illuminated with parallel light [2]. This modification allows variation of the monochromator higher order content or resolution, spot size without changing the focus. The performance of the beamline was investigated using various programs available at BESSY. The Undulator character- istics were evaluated using both SMUT and WAVE, and the optical performance of the monochromator was checked using REFLEC and RAY. The calculations show a resolving power of 2×104 with a flux of the order 1013 photons s-1 over the energy range covered by the mono- chromator. The maximum nominal second order contributions are ≈ 2\% at 300 eV for the first Undulator harmonic and ≈ 9\% for the third harmonic at 500 eV, both of which can be reduced by increasing the grating incidence angle and, or decreasing the Undulator Pinhole size.}, 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{HoffmannBoehmeSchmeisseretal., author = {Hoffmann, Patrick and B{\"o}hme, Oliver and Schmeißer, Dieter and Lloyd Spetz, Anita and M{\aa}rtenson, Per}, title = {Einfluß von Nanopartikeln auf die Funktion von Hochtemperatursensoren}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {Es werden Untersuchungen an als Hochtemperatur-Sensoren arbeitenden Schottky-Dioden mit dem Aufbau Metall-Oxidschicht-Siliziumkarbid vorgestellt. Dazu wurden Tiefenprofile mit XPS durch abwechselndes Abtragen durch Sputtern und Messen erstellt. Die Messungen erfolgten an thermisch unterschiedlich vorbehandelten Proben. Dabei konnten dipol-bedingte Verschiebungen der Bindungsenergie von Rumpfniveaus beobachtet werden. Das dazu notwendige Dipol-Moment wird durch das Entstehen von mit einer Oxidschicht {\"u}berzogenen Nanoteilchen erkl{\"a}rt. Die unterschiedlich ausgepr{\"a}gten Dipol-Verschiebungen auf den einzelnen Proben erlaubten eine Erkl{\"a}rung der thermischen Vorbehandlung, die bei Weglassen zu „frischen" und je nach Temperatur zu „aktivierten" oder „toten" Sensoren f{\"u}hrte.}, language = {de} }