Swiderek, Petra
Lade...
Preferred name
Swiderek, Petra
Official Name
Swiderek, Petra
5 Ergebnisse
Gerade angezeigt 1 - 5 von 5
- Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Elektronen-induzierte Reaktionen von Koordinationspolymeren zur Nanostrukturierung von Oberflächen(2019-04-26); ; ; Electron-induced reactions play a central role in the development of current methods for nanostructuring of surfaces. The basic principle is the decomposition of metal-containing compounds by a focused electron beam. In the present work the electron-induced reactions of three different copper-containing materials, namely, copper(II) oxalate, copper(II) squarate, and copper(II) 1,3,5-benzenetricarboxylate, were examined in detail. Reflection absorption infrared spectroscopy (RAIRS) and X-ray photoelectron spectroscopy (XPS) were used to identify chemical surface species that are formed upon electron exposure. To determine volatile decomposition products the electron-stimulated desorption (ESD) of neutral fragments was monitored with a new designed UHV setup. In addition, morphological changes of the samples were investigated by helium ion microscopy (HIM). It was shown that the molecular structure of the used anions is decisive for the efficiency and the outcome of the electron-induced decomposition. As an example, surface-bound layers of copper(II) oxalate were identified as suitable precursors for the production of metallic nanoparticles.Dissertation338 492 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Untersuchungen zum Ursprung der Homochiralität am Beispiel der Aminosäuren(2007-10-19); ; ; The question of the origin of homochirality, life's strange habit of using only one out of two possible enantiomers in many of its molecular building blocks, is closely related to the question of the origin of life itself. In this cumulative thesis composed of five research papers and a book-chapter, photochemical concepts for introducing a chiral bias in amino acids are discussed. The results of two different sets of experiments with circularly polarized VUV radiation, namely asymmetric photosynthesis and asymmetric photolysis, are given. Furthermore evidence for the presence of several diamino acids, a class of substances relevant for the evolution of a possible early form of genetic material called PNA, in meteorites is presented and calculations of their chiroptical properties are presented and discussed.Dissertation285 171 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Elektroneninduzierte Reaktionen in dünnen organischen Molekülfilmen(2006-12-21); ; ; This work provides an insight in the mechanisms of electron-induced reactions of thin films. For this, different organic substances were investigated using HREEL spectroscopy and products formed during bombardment were identified. Most of the substances are modified significantly when the incident electron energy is increased above 10 eV.Simple hydrocarbons like methane, ethane and ethylene seem to be relative stable with respect to electron bombardment. Aldehydes (acet- (AA), propion- (PA) and butyraldehyde (BA)) release CO. Other fragments formed together with CO react with adjacent molecules to a produce longer aldehydes. In the case of cyclic ethers (ethlyeneoxide (EO) and tetrahydrofurane (THF)), the main product is an aldehyde which reacts further to yield CO and unsaturated products. Other less prominant products are alcoholic substances or the enolic form of the aldehyde. After longer bombardment of EO a network is formed.In addition, cross sections were determined in the case of THF to give information about a reaction sequence. It was shown, that CO is not only formed from the initially produced aldehyde but also from THF itself.The investigation of gamma-butyrolactone (GBL) aimed at linking known gas phase results to the condensed phase. A charging during bombardment with low-energy electrons indicates the production of negative intermediates in the condensed phase. However, no products could be identified unequivocally. At high energies the formation of ethylene was observed and ascribed to successive CO release, with PA as intermediate.Finally acetonitrile was studied as a potential agent for the functionalization of surfaces during bombardment with electrons. The chemisorption of CH2CN fragments on diamond through Cdiam-C and Cdiam-N linkages was observed and a reaction mechanism was formulated.Dissertation233 132 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Kontrolle chemischer Reaktionen mit Elektronenstrahlung(2014-03-18); ; ; Interaction between low-energy electrons and molecules can lead to dissociative electron attachment (DEA) or dissociative ionization (DI). In condensed matter, the resulting reactive fragments can attack adjacent molecules to yield larger products. In this thesis, reactions initiated by DEA to acetonitrile in condensed phase have been compared to the known gas phase fragmentation channels. Also, gas phase DEA experiments have been performed on chlorosilanes to study the effect of a variation of the organic ligands on the energy of their molecular orbitals and reactivity in DEA processes. Furthermore, hydroamination reactions induced by DI for different alkenes and amines have been investigated. A similar reaction of ammonia and carbon monoxide was shown to produce formamide (HCONH2), which is the smallest molecule to contain a peptide bond and thus represents an important building block of biologically relevant substances.Dissertation269 134 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Funktionalisierung von selbstorganisierten Monolagen durch Bestrahlung mit niederenergetischen Elektronen(2014-03-10); ; ; The functionalisation of surfaces by the transformation of structurally simple molecules is one challenge of chemical research. The introduction of a specific functional group is an essential step towards this aim. Amino groups are very valuable because they can be used as linkers to connect complex molecules to the surface. One important aim of my thesis is to identify electron-induced reactions that lead to an attachment of such functional groups to simpler molecules. Previous studies had suggested that radicals produced under low-energy electron exposure of molecular films deposited on surfaces undergo further reactions that lead to activation of adjacent molecules and recombination with remaining radicals. We thus attempted to trigger a similar reaction that would introduce amino groups into a hydrocarbon by an electron-induced dissociation of NH3 yielding NH2 and H fragments in a mixture of NH3 with other molecules like ethane (C2H6). H was assumed to activate C2H6 by abstraction of another H so that, subsequently, the NH2 fragment could recombine with the resulting C2H5 fragment to produce C2H5NH2. Similarly, radicals produced by dissociation of the other molecules were also expected to recombine with NH2. In my thesis, it is shown that, instead of initiating the expected reactions, electron exposure of NH3 as pure film and in mixtures leads to production of N2 and desorption of both the starting material and the product. If, on the other hand, ethylene is used as a hydrocarbon component, exposure at energies above the ionisation threshold leads to formation of C2H5NH2. This reaction is reminiscent of a hydroamination known from organic chemistry with the difference that the electron replaces the catalyst used in the organic synthesis. The latter is required to lower the activation barrier that results from the electrostatic repulsion between neutral C2H4 and NH3. This repulsion can also be eliminated by ionisation of one of the reaction partners. Therefore, the present finding provides evidence that soft ionisation is an alternative strategy to control the outcome of electron-induced reactions. In my work it is shown that a similar reaction can be used for the functionalisation of a self-assembled monolayer.Dissertation283 132