In der vorliegenden Dissertation werden Dünnschichten des Oberflächenproteins (Surface (S)-Layer) des Bacillus sphaericus NCTC 9602 auf einem SiOx-Substrat mittels Photoemission (PE) und Röntgenabsorptionsspektroskopie untersucht. Sowohl die PE-Daten als auch die Nahkantenabsorptionsspektren (NEXAFS) sind in qualitativer und quantitativer Übereinstimmung mit der erwarteten elektronischen Struktur des S-Layers, was auf eine weitgehende Stabilität des Systems gegenüber den Messbedingungen (Vakuum, Röntgenstrahlung) hindeutet. Mittels resonanter Photoemission war es möglich, die einzelnen Valenzbandstrukturen individuellen chemischen Bindungen zuzuordnen. Aus dem Vergleich der Intensitäten von Participator- und Spectator- Übergängen konnte ferner die Zeitskala für Elektronenhüpfprozesse innerhalb des LUMO (Lowest Unoccupied Molecular Orbital, niedrigstes unbesetztes Molekülorbital) zu 100 fs abgeschätzt werden, was in guter Übereinstimmung mit einem in der Literatur vorgeschlagenen, auf Drehschwingungen basierenden Transportmechanismus ist. Der S-Layer wurde im folgenden als Templat für die Erzeugung von Metallclustern genutzt, die sich bei physikalischer Deposition reiner Metalle (Ag, Co) ausbilden. Elektronenmikroskopische Untersuchungen zeigen, dass sich im Fall nominaler Silberbedeckungen im Monolagenbereich Cluster von der Größe einiger nm bilden, die sich auf einem quadratischen Übergitter mit einer Kantenlänge von 14 nm anordnen. Die spektroskopischen Daten weisen die Sauerstoffatome der Peptidketten als wahrscheinlichste Adsorptionsplätze aus. Während die Ag-Cluster sich weitgehend nicht-reaktiv verhalten, zeigen Co-Cluster deutlich stärkere Wechselwirkung mit dem Templat. Unter Nutzung eines im NEXAFS-Mode betriebenen Photoelektronenmikroskops (PEEM) wurde schließlich die Schädigung reiner und Cluster bedeckter S-Layer bei intensiver Röntgenbestrahlung untersucht. Die Schädigung ist im Fall der Clusterbedeckung deutlich niedriger als bei reinen Oberflächen. Ein nur auf Abschattung des Templats durch die Cluster beruhendes Modell beschreibt die spektroskopischen Daten jedoch nicht zufriedenstellend. Vielmehr müssen Schädigungen des Templats durch Elektronen, die infolge Röntgenabsorption innerhalb der Cluster generiert werden, mit berücksichtigt werden.:1. Einführung 3 2. Theoretische Grundlagen der Messmethoden 7 2.1 Photoelektronenspektroskopie . . . . . . . . . . . . . . . . . . . . . . 7 2.1.1 Wirkungsquerschnitt der Photoionisation . . . . . . . . . . . . 13 2.1.2 Valenzbandspektroskopie . . . . . . . . . . . . . . . . . . . . . 14 2.1.3 Rumpfniveauspektroskopie und Rumpfniveauverschiebung . . 15 2.1.4 Nahkantenabsorptionsspektroskopie . . . . . . . . . . . . . . . 18 2.1.5 Resonante Photoemission . . . . . . . . . . . . . . . . . . . . 20 2.2 Elektronenmikroskopie . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.3 Photoelektronenmikroskopie . . . . . . . . . . . . . . . . . . . . . . . 26 3. Bakterielle Oberflächenproteine 29 3.1 Aufbau und Struktur der S-Layer . . . . . . . . . . . . . . . . . . . . 30 3.2 Reassemblierung von Bacillus sphaericus NCTC 9602 . . . . . . . . . . 32 4. Experimentelle Details und Probenpräparation 37 4.1 Aufbau der Ultrahochvakuumapparaturen . . . . . . . . . . . . . . . 37 4.1.1 Deutsch-Russisches-Strahlrohr . . . . . . . . . . . . . . . . . . 38 4.1.2 PEEM-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 4.2 Probenpräparation und Durchführung der Metallisierung . . . . . . . 41 5. Elektronische Struktur des S-Layers 43 5.1 Rumpfniveauspektroskopie . . . . . . . . . . . . . . . . . . . . . . . 43 5.2 Valenzbandspektroskopie . . . . . . . . . . . . . . . . . . . . . . . . . 48 5.3 Lateral integrierte NEXAFS-Spektroskopie . . . . . . . . . . . . . . . 51 5.3.1 Das C 1s-NEXAFS-Spektrum des S-Layers . . . . . . . . . . . 52 5.3.2 Das N 1s- und O 1s-NEXAFS-Spektrum des S-Layers . . . . . 53 5.4 Lateral aufgelöste NEXAFS-Spektroskopie - PEEM Studien . . . . . 56 5.4.1 C 1s-, O 1s- und N 1s-NEXAFS-Messungen . . . . . . . . . . 60 2 Inhaltsverzeichnis 5.5 Resonante Photoemission . . . . . . . . . . . . . . . . . . . . . . . . . 62 5.5.1 Einfluss der Seitenketten auf elektronische Struktur . . . . . . 63 6. Strahlenschäden an Biomolekülen 66 6.1 Einfluss von Röntgenstrahlung auf das Oberflächenprotein . . . . . . 67 7. Ladungstransport in Proteinen 80 7.1 Ladungslokalisierung im Biomolekül . . . . . . . . . . . . . . . . . . . 82 8. Protein-Metall Hybridstrukturen und deren Synthese auf S-Layern 92 8.1 Protein-Silber Hybridstruktur . . . . . . . . . . . . . . . . . . . . . . 93 8.1.1 Rumpfniveauspektroskopie . . . . . . . . . . . . . . . . . . . . 93 8.1.2 PEEM - Studie . . . . . . . . . . . . . . . . . . . . . . . . . . 99 8.1.3 Elektronische Struktur der Silber-Nanopartikel . . . . . . . . . 102 8.1.4 TEM-Studien . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 8.2 Protein-Cobalt Hybridstruktur . . . . . . . . . . . . . . . . . . . . . . 109 8.2.1 Vergleichende PEEM-Studie . . . . . . . . . . . . . . . . . . . 109 8.3 Strahlenschäden an Protein-Metall Hybridstrukturen . . . . . . . . . .114 8.3.1 Diskussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 9. Zusammenfassung 119 A Anhang 121 A1 Anbindung von Metallatomen an eine Peptidkette . . . . . . . . . . . 121 Abbildungsverzeichnis 122 Tabellenverzeichnis 129 Literaturverzeichnis 133 Danksagung 141

Les sols stockent trois fois plus de carbone que l'atmosphère sous la forme d'un mélange de molécules, la matière organique des sols (MOS). Certaines de ces molécules sont présentes dans le sol depuis des centaines voire des milliers d'années. Trois mécanismes de protection sont utilisés pour expliquer cette persistance à long terme des matières organiques dans les sols : (i) la récalcitrance chimique, (ii) la protection physique dans les agrégats et (iii) la protection physicochimique par adsorption sur les surfaces minérales. Le but de ce projet de thèse est d’améliorer la compréhension de ces processus de protection et de leur importance relative. Mon projet de thèse utilise des échantillons permettant l'accès au carbone persistant : les jachères nues de longue durée (5 sites en Europe). Il s'agit de parcelles maintenues vierges de toute végétation dans lesquelles, au fur et à mesure de la biodégradation, la quantité totale de carbone diminue, entraînant un enrichissement relatif en carbone persistant. La première étude expérimentale de ce travail de thèse vise à tester l'efficacité des méthodes d'oxydation chimique. Les deux réactifs les plus couramment utilisés -l'hypochlorite de sodium NaOCl et le peroxyde d'hydrogène H2O2- ont été testés sur des échantillons de la plus longue jachère nue (Versailles). Il est conclu que les méthodes d'oxydation chimique n'arrivent pas à isoler efficacement un réservoir de carbone persistant à l'échelle du siècle.En termes de mécanismes de persistance, les résultats obtenus montrent que la récalcitrance chimique n'est pas le principal mécanisme de protection. En effet, sur la durée de la jachère nue, la composition chimique de la MOS, caractérisée par spectroscopie NEXAFS, ne présente que peu de changements. Un enrichissement en composés présentant des groupements acides carboxyliques est détecté pour tous les sites testés. Une étude poussée de la persistance spécifique du carbone pyrogénique des sols a aussi été réalisée, ces composés sont actuellement considérés cinq fois plus persistants que le carbone total. Les résultats montrent que le carbone pyrogénique est moins persistant que prévu. En effet, le temps de résidence moyen du carbone pyrogénique obtenu par la méthode BPCA (116 ans) est seulement 1,6 fois supérieur à celui de la MOS (73 ans). L'étude du contrôle minéralogique de la persistance des MOS montre que les argiles contenant du potassium (illite) protègent moins de carbone que les argiles smectitiques. Le rapport C/N décroit avec le temps dans toutes les fractions argiles, ce qui prouve que les composés riches en azote sont préférentiellement préservés. Enfin, la présence de microagrégats dans la fraction grossière des argiles implique la coexistence de deux mécanismes de protection : la protection physique et la protection par adsorption sur les minéraux. / Soils store three times more carbon than the atmosphere, under the form of a complex mixture of molecules called soil organic matter (SOM). Some of these molecules have been standing in the soil for hundreds to thousands of years. Three main mechanisms are invoked to explain this long term carbon persistence in soils, (i) chemical recalcitrance, (ii) physical protection in aggregates and (iii) protection by adsorption on mineral surfaces. One of the major challenges in SOM science is to better understand the relative importance of each mechanism, that is the aim of this PhD project. Here, we use samples from by long term bare fallows (5 sites across Europe). These experimental plots have been kept free of vegetation by manual or chemical weeding for several decades and have been regularly sampled and stored. As the duration of the bare fallow increases, biodegradation occurs and samples get enriched in persistent carbon.First experiments consisted in testing the efficiency of chemical oxidations (two reagent were tested, sodium hypochlorite –NaOCl- and hydrogen peroxide –H2O2) on the longest bare fallow. We concluded that oxidation methods were not able to efficiently isolate a pool of persistent carbon at the centennial timescale. In terms of mechanisms of persistence, the obtained results show that chemical recalcitrance does not seem to be the major mechanism. Indeed, over the duration of the bare fallow, the chemical composition of SOM, as seen by synchrotron based NEXAFS spectroscopy, shows little changes. There is a consistent increase in carboxylics for all sites (12% increase on average) though it is significant for 2 out of the 4 selected sites. We also studied the particular persistence of soil pyrogenic carbon, which is thought to be at least five times more persistent than bulk SOM. Results show that pyrogenic carbon lacks long term persistence. Indeed the BPCA-estimated mean residence time of pyrogenic carbon (116 years) is on average 1.6 times longer than MRT for bulk SOM (73 years). Finally, the study of mineralogical control of the persistence of SOC showed that clay minerals containing potassium (illite) seemed to protect less carbon. As seen by NEXAFS-STXM, more mineral surfaces with very little SOM appear with the duration of bare fallow. C:N ratio decreased in all clay fractions, suggesting a preferential persistence of N-rich compounds. Presence of microaggregates in the coarser clay fraction led to the coexistence of two protection mechanisms: adsorption and physical protection.

Currently, automotive batteries use intercalation cathodes such as lithium iron phosphate (LiFePO4) which provide high levels of safety while sacrificing cell voltage and therefore energy density. Lithium transition metal oxide (LiMO2) batteries achieve higher cell voltages at the risk of releasing oxygen gas during charging, which can lead to ignition of the liquid electrolyte. To achieve both safety and high energy density, oxide cathodes must be well characterized under operating conditions. In any intercalation cathode material, the loss of positive lithium ions during charge must be balanced by the loss of negative electrons from the host material. Ideally, the TM ions oxidize to compensate this charge. Alarmingly, the stoichiometry of the latest LiMO2 cathode materials includes more lithium ions than the TM ions can compensate for. Inevitably, peroxide ions or dioxygen gas must form. The former mechanism is vital for lithium-air batteries, while the latter must be avoided. Battery researchers have long sought to completely characterize the intercalation reaction in working batteries. However, the volatile electrolytes employed in batteries are not compatible with vacuum-based characterization techniques, nor are the packaging materials required to contain the liquid. For the first time, a solid state battery (using exposed particles of Li1.17Ni0.25Mn0.58O2) was charged while using soft X-ray absorption spectroscopy to observe the redox trends in nickel, manganese and oxygen. This was combined with innovative hard X-ray absorption spectroscopic studies on the same material to create the most complete picture yet possible of charge compensation.

Taking into account the technological demand for the controlled preparation of atomically precise graphene nanoribbons (GNRs) with well-defined properties, the present thesis is focused on the investigation of the role of the underlying metal substrate in the process of building GNRs using bottom-up strategy and on the changes in the electronic structure of GNRs induced by the GNR-metal interaction. The combination of surface sensitive synchrotron-radiation-based spectroscopic techniques and scanning tunneling microscopy with in situ sample preparation allowed to trace evolution of the structural and electronic properties of the investigated systems. Significant impact of the substrate activity on the growth dynamics of armchair GNRs of width N = 7 (7-AGNRs) prepared on inert Au(111) and active Cu(111) was demonstrated. It was shown that unlike inert Au(111) substrate, the mechanism of GNRs formation on Ag(111) and Cu(111) includes the formation of organometallic intermediates based on the carbon-metal-carbon bonds. Experiments performed on Cu(111) and Cu(110), showed that a change of the balance between molecular diffusion and intermolecular interaction significantly affects the on-surface reaction mechanism making it impossible to grow GNRs on Cu(110). It was demonstrated that deposition of metals on spatially aligned GNRs prepared on stepped Au(788) substrate allows to investigate GNR-metal interaction using angle-resolved photoelectron spectroscopy. In particular intercalation of one monolayer of copper beneath 7-AGNRs leads to significant electron injection into the nanoribbons, indicating that charge doping by metal contacts must be taken into account when designing GNR/electrode systems. Alloying of intercalated copper with gold substrate upon post-annealing at 200°C leads to a recovery of the initial position of GNR-related bands with respect to the Fermi level, thus proving tunability of the induced n-doping. Contrary, changes in the electronic structure of 7-AGNRs induced by the deposition of Li are not reversible.  It is demonstrated that via lithium doping 7-AGNRs can be transformed from a semiconductor into a metal state due to the partial filling of the conduction band. The band gap of Li-doped GNRs is reduced and the effective mass of the conduction band carriers is increased.

The present thesis is focused on various methods of controlling electronic and geometrical structure of two-dimensional overlayers adsorbed on metal surfaces exemplified by graphene and hexagonal boron nitride (h-BN) grown on transition metal (TM) substrates. Combining synchrotron-radiation-based spectroscopic and various microscopic techniques with in situ sample preparation, we are able to trace the evolution of overlayer electronic and geometrical properties in overlayer/substrate systems, as well as changes of interfacial interaction in the latter.It is shown that hydrogen uptake by graphene/TM substrate strongly depends on the interfacial interaction between substrate and graphene, and on the geometrical structure of graphene. An energy gap opening in the electronic structure of graphene on TM substrates upon patterned adsorption of atomic species is demonstrated for the case of atomic oxygen adsorption on graphene/TM’s (≥0.35 eV for graphene/Ir(111)). A non-uniform character of adsorption in this case – patterned adsorption of atomic oxygen on graphene/Ir(111) due to the graphene height modulation is verified. A moderate oxidation of graphene/Ir(111) is found largely reversible. Contrary, oxidation of h-BN/Ir(111) results in replacing nitrogen atoms in the h-BN lattice with oxygen and irreversible formation of the B2O3 oxide-like structure.      Pronounced hole doping (p-doping) of graphene upon intercalation with active agents – halogens or halides – is demonstrated, the level of the doping is dependent on the agent electronegativity. Hole concentration in graphene on Ir(111) intercalated with Cl and Br/AlBr3 is as high as ~2×1013 cm-2 and ~9×1012 cm-2, respectively.     Unusual periodic wavy structures are reported for h-BN and graphene grown on Fe(110) surface. The h-BN monolayer on Fe(110) is periodically corrugated in a wavy fashion with an astonishing degree of long-range order, periodicity of 2.6 nm, and the corrugation amplitude of ~0.8 Å. The wavy pattern results from a strong chemical bonding between h-BN and Fe in combination with a lattice mismatch in either [11 ̅1] or [111 ̅] direction of the Fe(110) surface. Two primary orientations of h-BN on Fe(110) can be observed corresponding to the possible directions of lattice match between h-BN and Fe(110).     Chemical vapor deposition (CVD) formation of graphene on iron is a formidable task because of high carbon solubility in iron and pronounced reactivity of the latter, favoring iron carbide formation. However, growth of graphene on epitaxial iron films can be realized by CVD at relatively low temperatures, and the formation of carbides can be avoided in excess of the carbon-containing precursors. The resulting graphene monolayer creates a periodically corrugated pattern on Fe(110): it is modulated in one dimension forming long waves with a period of ~4 nm parallel to the [001] direction of the substrate, with an additional height modulation along the wave crests. The novel 1D templates based on h-BN and graphene adsorbed on iron can possibly find an application in 1D nanopatterning. The possibility for growing high-quality graphene on iron substrate can be useful for the low-cost industrial-scale graphene production.

The polyphenol pathway and Maillard reaction (polycondensation of sugars and amino acids) are regarded as important pathways in natural humification. The significance of linking the Maillard reaction and polyphenol pathways into an integrated humification pathway has been addressed. However, the ability of mineral colloids commonly occurring in tropical and temperate environments to promote the Maillard reaction and integrated polyphenol-Maillard humification pathways remained to be uncovered. Furthermore, the effect of the nature and relative abundance of biomolecules on humification and associated reaction products remained to be studied.<p>The results of this study show that the structure of polyphenols and the relative molar ratio of polyphenol, glucose and glycine, significantly affected humification processes and the associated carbonate formation in the integrated polyphenol-Maillard reaction catalyzed by birnessite. Increasing the molar ratio of ortho-polyphenols (catechol and pyrogallol) to Maillard reagents in the polyphenol-Maillard pathway catalyzed by birnessite enhanced humification while suppressing the formation of rhodochrosite (MnCO3). The opposite trend of MnCO3 formation was observed in the meta-polyphenol (resorcinol)-Maillard reaction system. Increasing the amount of glucose in the integrated catechol-Maillard system under the catalysis of birnessite promoted the formation of Maillard reaction-type humic acid in the supernatant and MnCO3 in the solid phase.<p>The catalytic abilities of commonly occurring mineral colloids from temperate and tropical regions greatly differed in influencing humification processes and products in the Maillard reaction and integrated polyphenol-Maillard pathways. Compared with layer silicate colloids, the poorly ordered Fe and Mn oxides were by far the strongest catalysts of humification reactions in the Maillard and catechol-Maillard pathways. This accounted for the significant difference in reactivity between the sesquioxide-rich Oxisol clay from the high rainfall region of South Africa and the Mollisol clay from the Canadian Prairies. Furthermore, the nature of the mineral colloids also affected the extent of organic C accumulation in the solid phase upon humification, and related mineral surface alteration. The metal oxide- and Oxisol clay-catalyzed Maillard and catechol-Maillard reaction systems had the highest accumulation of organic C in the solid phase, indicating their significance in contributing to C sequestration in the environment.<p>The findings obtained in this study are of fundamental significance in understanding the influence of the atomic bonding, structural configuration and related surface properties of mineral colloids, and the nature and abundance of biomolecules on the abiotic humification pathways and related reaction products in natural environments.

A novel method by which to calculate the near edge X-rayabsorption fine structure region of the X-ray absorption spectrum has been derived and implemented. By means of damped coupled cluster theory at coupled cluster levels CCS, CC2, CCSD and CCSDR(3), the spectra of neon and methane have been investigated. Using methods incorprating double excitations, the important relaxation effects maybe taken into account by simultaneous excitation of the core electron and relaxation of other electrons. An asymmetric Lanczos-chain driven approach has been utilized as a means to partially resolve the excitation space given by the coupled cluster Jacobian. The K-edge of the systems have been considered, and relativistic effects are estimated with use of the Douglas--Kroll scalar relativistic Hamiltonian. Comparisons have been made to results obtained with the four-component static-exchange approach and ionization potentials obtained by the {Delta}SCF-method. The appropriate basis sets by which to describe the core and excited states have been been determined.  The addition of core-polarizing functions and diffuse or Rydberg functions is important for this description. Scalar relativistic effects accounts for an increase in excitation energies due to the contraction of the 1s-orbital, and this increase is seen to be 0.88 eV for neon. The coupled cluster hierachy shows a trend of convergence towards the experimental spectrum, with an 1s -&gt; 3p excitation energy for neon of an accuracy of 0.40 eV at a relativistic CCSDR(3) level of theory. Results obtained at the damped coupled cluster and STEX levels of theory, respectively, are seen to be in agreement, with a mere relative energy shift.

The polyphenol pathway and Maillard reaction (polycondensation of sugars and amino acids) are regarded as important pathways in natural humification. The significance of linking the Maillard reaction and polyphenol pathways into an integrated humification pathway has been addressed. However, the ability of mineral colloids commonly occurring in tropical and temperate environments to promote the Maillard reaction and integrated polyphenol-Maillard humification pathways remained to be uncovered. Furthermore, the effect of the nature and relative abundance of biomolecules on humification and associated reaction products remained to be studied.<p>The results of this study show that the structure of polyphenols and the relative molar ratio of polyphenol, glucose and glycine, significantly affected humification processes and the associated carbonate formation in the integrated polyphenol-Maillard reaction catalyzed by birnessite. Increasing the molar ratio of ortho-polyphenols (catechol and pyrogallol) to Maillard reagents in the polyphenol-Maillard pathway catalyzed by birnessite enhanced humification while suppressing the formation of rhodochrosite (MnCO3). The opposite trend of MnCO3 formation was observed in the meta-polyphenol (resorcinol)-Maillard reaction system. Increasing the amount of glucose in the integrated catechol-Maillard system under the catalysis of birnessite promoted the formation of Maillard reaction-type humic acid in the supernatant and MnCO3 in the solid phase.<p>The catalytic abilities of commonly occurring mineral colloids from temperate and tropical regions greatly differed in influencing humification processes and products in the Maillard reaction and integrated polyphenol-Maillard pathways. Compared with layer silicate colloids, the poorly ordered Fe and Mn oxides were by far the strongest catalysts of humification reactions in the Maillard and catechol-Maillard pathways. This accounted for the significant difference in reactivity between the sesquioxide-rich Oxisol clay from the high rainfall region of South Africa and the Mollisol clay from the Canadian Prairies. Furthermore, the nature of the mineral colloids also affected the extent of organic C accumulation in the solid phase upon humification, and related mineral surface alteration. The metal oxide- and Oxisol clay-catalyzed Maillard and catechol-Maillard reaction systems had the highest accumulation of organic C in the solid phase, indicating their significance in contributing to C sequestration in the environment.<p>The findings obtained in this study are of fundamental significance in understanding the influence of the atomic bonding, structural configuration and related surface properties of mineral colloids, and the nature and abundance of biomolecules on the abiotic humification pathways and related reaction products in natural environments.

Die Arbeit befaßt sich mit der Charakterisierung der elektronischen Struktur von neuen Halbleitermaterialien. Zu den untersuchten Materialsystemen, welche alle eine relativ kleine Gitterkonstante aufweisen, gehören der Diamant, Siliciumcarbid, amorphes Kohlenstoffnitrid (a-CNx) sowie verschiedene Proben der Serie AlxGa1-xN. Zur Charakterisierung der elektronischen Struktur werden Photoemissionsmessungen für die Bestimmung der besetzten Zustände und Methoden der Röntgenabsorption im Fall der unbesetzten Zustände herangezogen. Mit diesen Methoden wird die Struktur der Oberflächen von CVD-Diamantfilmen für unterschiedliche Oberflächenempfindlichkeiten bestimmt. Außerdem wird die Modifikation der elektronischen Bänder in Naturdiamant durch variierende Cäsiumbedeckungen der Oberfläche ermittelt. Für zwei Rekonstruktionen der 3C-SiC(001)-Oberfläche wird die Oberflächenbandstruktur bestimmt und es werden die Ergebnisse mit existierenden Strukturmodellen und Rechnungen verglichen. Zum Vergleich werden auf dieser Oberfläche weiterhin auch Messungen zur optischen Oberflächenanisotropie durchgeführt und Hinweise auf Beiträge von Oberflächenzuständen zu den Spektren gefunden. In den amorphen Kohlenstoffnitridfilmen können verschiedene Stickstoff- und Kohlenstoffkoordinationen nachgewiesen und deren Temperaturstabilität bestimmt werden. Aus den polarisationsabhängigen Röntgenabsorptionsmessungen an nitridiertem Galliumarsenid bzw. an den Proben der Serie AlxGa1-xN werden Rückschlüsse auf die Phasenzusammensetzung und die geometrische Struktur gezogen.

The present thesis investigates the electronic and structural properties of adenine, cytosine, and guanine layers on hydrogen passivated silicon (111)(7x7). The (7x7) reconstruction of the silicon surface was achieved by direct current heating of the samples in UHV conditions. After in situ hydrogen passivation layers of the DNA bases were prepared in different thicknesses by means of organic molecular beam deposition, all samples were characterized employing valence band and core level photoemission spectroscopy. Additionally the near edge x-ray absorption fine structure of the DNA base layers was investigated. A detailed and consistent picture of structural and electronic properties of the nucleotide bases in the solid state could be developed by comparison of measurements and DFT/B3LYP calculations.