<p>This thesis presents experimental studies of gas phasemolecular relaxation after excitation with synchrotron photonsin the 15-35 eV and in the 70-350 eV regions.</p><p>In the 15-35 eV region, molecular relaxation by neutraldissociation processes and non</p><p>Franck-Condon effects in N2 and O2 molecules have beenstudied by means of dispersed fluorescence and photoelectronspectroscopy experimental techniques, respectively. From thedispersed fluorescence data, excitation functions for themeasured atomic fluorescence spectra have been obtained. Fromthe recorded photoelectron spectra vibrational branching ratioshave been produced. The results obtained reveal that Rydbergseries and singly and doubly excited valence states of theappropriate symmetry energetically accessible in the studiedregion and interactions between themaccount for most of theobserved effects in these two type of experiments.</p><p>In the 70-350 eV range, molecular relaxation processesresulting in fragmentation of CD4 and SF6 after absorption ofsynchrotron light have been studied by energy resolved electronion coincidence technique using a multicoincidence experimentalstation developed by our group during the last five years forsuch type of experiments. The coincidence measurements yieldedmass spectra from which information about the kinematics of thedetected fragments has been deduced by means of Monte Carlosimulations of the experimental peak shapes. The obtainedresults show completely different dissociation patternsdepending on the molecular electronic states studied. Thesepatterns reflect the bonding properties of the excited orbitalsand they permit the description and in some cases theidentification of the different molecular relaxation pathwaysobserved. The achievements presented in this thesis exemplifythe potential of the multicoincidence station used in thereported experiments.</p>

Although silicon (Si) nanostructures exhibit size dependent light emission, which can be attributed to quantum confinement, the role of surface passivation is not yet fully understood. This understanding is central to the development of nanocrystal-based detectors. This study investigated the growth, surface chemistry, passivation with deuterium (D2), ammonia (ND3) and diborane (B2D6) and the resulting optical properties of Si nanostructures. Si nanocrystals less than 6 nm in diameter are grown on SiO2 surfaces in an ultra high vacuum chamber using hot-wire chemical vapor deposition and the as grown surfaces are exposed to atomic deuterium. Temperature programmed desorption (TPD) spectra show that that the nanocrystals surfaces are covered by a mix of monodeuteride, dideuteride and trideuteride species. The manner of filling of the deuteride states on nanocrystals differs from that for extended surfaces as the formation of the dideuteride and trideuteride species is facilitated by the curvature of the nanocrystal. No photoluminescence (PL) is observed from the as grown unpassivated nanocrystals. As the deuterium dose is increased, the PL intensity also begins to increase. This can be associated with increasing amounts of mono-, di- and trideuteride species on the nanocrystal surface, which results in better passivation of the dangling bonds and relaxing of the reconstructed surface. At high deuterium doses, the surface structure breaks down and amorphization of the top layer of the nanocrystal takes place. Amorphization reduces the PL intensity. Finally, as the nanocrystal size is varied, the PL peak shifts, which is characteristic of quantum confinement. The dangling bonds and the reconstructed bonds at the NC surface are also passivated and transformed with D and NDx by using deuterated ammonia (ND3), which is predissociated over a hot tungsten filament prior to adsorption. At low hot wire ND3 doses PL emission is observed at 1000 nm corresponding to reconstructed surface bonds capped by predominantly monodeuteride and Si-ND2 species. As the hot wire ND3 dose is increased, di- and trideuteride species form and intense PL is observed around 800 nm that does not shift with NC size and is associated with defect levels resulting from NDx insertion into the strained Si-Si bonds forming Si2=ND. The PL intensity at 800 nm increases as the ND3 dose is increased and the intensity increase is correlated to increasing concentrations of deuterides. At extremely high ND3 doses PL intensity decreases due to amorphization of the NC surface. In separate experiments, Si NCs were subjected to dissociative (thermal) exposures of ammonia followed by exposures to atomic deuterium. These NCs exhibited size dependent PL and this can be attributed to the prevention of the formation of Si2=ND species. Finally, deuterium-passivated Si NCs are exposed to BDx radicals formed by dissociating deuterated diborane (B2D6) over a hot tungsten filament and photoluminescence quenching is observed. Temperature programmed desorption spectra reveal the presence of low temperature peaks, which can be attributed to deuterium desorption from surface Si atoms bonded to subsurface boron atoms. The subsurface boron likely enhances nonradiative Auger recombination. / text

This work describes the synthesis of dendrimer-encapsulated nanoparticles (DENs) and the expansion of the characterization ability for these materials. The dendrimer-template method for the synthesis of nanoparticles allows precise control over the size, composition and structure of nanoparticles in the 40-250 atom range. In this size regime, the surface structure of the nanoparticles dominates their catalytic properties. The long term goal of this research is to correlate the structure of these nanoparticles to their catalytic activity, improving the ability to predict superior catalysts a priori. As a prerequisite for this analysis, the precise structure of the catalytically active nanoparticle must be determined. Characterization of nanoparticles in the 1-2 nm region is significantly more difficult than more commonly used nanoparticles of 3-5 nm diameter or larger. Typical characterization of these nanoparticles involves UV-vis spectroscopy for Mie absorbance and transmission electron microscopy for size analysis. This work involves the use of extended X-ray absorption-fine structure (EXAFS) to determine the local structure of the nanoparticles. For monometallic Pt DENs, EXAFS was combined with UV-vis, TEM, X-ray photoelectron spectroscopy (XPS) and electrochemistry to determine that the Pt system is not simply nanoparticles but a more complex, bimodal state. EXAFS has also been used to differentiate between different bimetallic structures. For PdAu DENs, there are two synthetic methods used. When both metals are reduced simultaneously, the resulting nanoparticles have a quasi-random alloy structure. These nanoparticles were then extracted from the dendrimer into an organic solvent by use of alkanethiols. The extraction process changed the alloy structure into Au-core/Pd-shell. When Pd and Au were reduced in sequence, the DENs were formed as a Au-core/Pd-shell material, regardless of the order of the reduction of the metals. The Au-core/Pd-shell structure was also present after extraction. In addition to structural analysis to determine the result of different synthetic methods, EXAFS was also used in situ to measure the structure of Pt DENs during the oxidation of absorbed CO. These in situ measurements are important for determining the structure of the actual catalyst rather than the precursor nanoparticle. In this case, the Pt DENs changed from a bimodal distribution into fully reduced nanoparticles by the application of a reducing potential. The binding of CO to the Pt DENs and subsequent oxidation did not cause measurable agglomeration of the nanoparticles. This reduction of the Pt system by electrochemical means was also explored as a synthetic method. The Pt-dendrimer complex was placed on a TEM grid for electrochemical treatment. A potential step was shown to reduce some of the Pt-dendrimer complexes into Pt nanoparticles of the expected size. However, most of the complexes were not reduced. Therefore, only the standard chemical reduction followed by electrochemical treatment is sufficient to fully reduce the nanoparticle samples. This work has explored additional synthetic methods for the synthesis of monometallic and bimetallic DENs. The use of EXAFS, as well as other advanced characterization techniques, has advanced knowledge of the structure of various DENs. Both the characterization toolset and the synthetic methods will provide a basis for investigations of catalytically active materials. / text

Στην παρούσα διπλωματική εργασία αναλύονται λεπτά υμένια (thin films) διαφόρων πολυμερικών ή ολιγομερών οργανικών ενώσεων, με την επεξεργασία μετρήσεων που είχαν ληφθεί με την επιφανειακά ευαίσθητη τεχνική της φασματοσκοπίας φωτοηλεκτρονίων από ακτίνες Χ (XPS). Από την ανάλυση των φασμάτων XPS προκύπτουν συμπεράσματα τόσο για την παρουσία συγκεκριμένων χημικών στοιχείων στα δείγματα (ποιοτική ανάλυση) όσο και για την συγκέντρωση των στοιχείων αυτών στην περιοχή ανάλυσης (ποσοτική ανάλυση). / This thesis analyzed thin films (thin films) various polymeric or oligomeric organic compounds, the processing of measurements taken with the surface sensitive technique of spectroscopy X-ray photoelectron (XPS). From the analysis of XPS spectra resulting conclusions as to the presence of certain chemical elements in samples (qualitative analysis) and for the concentration of these elements in the analysis (quantitative analysis).

Photovoltaics manufactured using organic materials as a substitute for inorganic materials may provide for cheaper production of solar cells if their efficiencies can be made comparable to existing technologies. Photovoltaic devices are comprised of layered structures where the electrical, chemical, and physical properties at the multiple interfaces play a significant role in the operation of the completed device. This thesis attempts to establish a relationship between interfacial properties and overall device performance by investigation of both the organic/organic heterojunction interface, as well as the interface between the inorganic substrate and the first organic layer with useful insights towards enhancing the efficiency of organic solar cells.It has been proposed that residual chemical species may act as barriers to charge transfer at the interface between the transparent conductor (TCO) and the first organic layer, possibly causing a large contact resistance and leading to reduced device performance. Previous work has investigated the surface of the TCO but no baseline characterization of carbon-free surfaces has previously been given. In this work clean surfaces are investigated to develop a fundamental understanding of the intrinsic spectra such that further analyses of contaminated surfaces can be presented systematically and reproducibly to develop a chemical model of the TCO surface.The energy level offset at the organic/organic heterojunction has been proposed to relate to the maximum potential achievable for a solar cell under illumination, however, few experimental observations have been made where both the interface characterization and device performance are presented. Photovoltaic properties are examined in this work with titanyl phthalocyanine used as a novel donor material for enhancement of spectral absorption and optimization of the open-circuit potential. Characterization of the interface between TiOPc and C60 coupled with characterization of the interface between copper phthalocyanine and C60 shows that the higher ionization potential of TiOPc does correlate to greater open circuit potentials.Examination of photovoltaic behavior using equivalent circuit modeling relates the importance of series resistance and recombination to the homogeneity of the solar cell structure.

The mechanism by which chiral selectivity takes place is complicated by the surface morphology, the possible involvement of the solvent, and the characteristics of the chiral molecules at the surface. My goal is to model and understand the factors which lead to significant discrimination in the case of three closely related chiral stationary phases: N-(1-phenylethyl)-N’-[3-(triethoxysilyl)propyl]-urea (PEPU), [(3,5-dinitrobenzoyl)-amino]-N-[3-(triethoxysilyl)propyl]-2-phenylacetamide (DNB-phenyglycine), and [(3,5-dinitrobenzoyl)amino]-N-[3-(triethoxysilyl)propyl]-4-methylpentanamide (DNB-leucine). Ab initio calculations are used to develop molecular models of these chiral selectors. These models are employed in molecular dynamics (MD) simulations, which provide the theoretical framework for modelling chiral interfaces in different solvent mixtures. The MD simulations of PEPU interfaces show that, in alcohol/water mixtures, the alcohols form domains at the interface with the hydrophobic portions of the molecule tending to orient towards the surface. This disrupts the water hydrogen bonding networks at the interface and leads to the exclusion of water from the surface region relative to the bulk. The MD simulations of DNB-phenylglycine and DNB-leucine selectors in hexane/2-propanol mixtures demonstrate that the interfaces are distinct both in terms of the selector orientations at the surface and in the number of hydrogen bonds formed with 2-propanol. This occurs despite the structural similarity between these two selectors. The interfaces are also prepared experimentally by attaching the chiral selectors onto oxidized Si(111) samples and AFM tips. In particular, for DNB-phenylglycine and DNB-leucine samples, two synthetic routes have been explored. Using AFM, the morphologies of the resulting chiral interfaces are obtained. X-ray photoelectron spectroscopy and refraction-absorption infrared spectroscopy provide information regarding the relative distribution of the compounds on the surface. Using chemical force microscopy (CFM) measurements, chiral self-selectivity is examined in various solvent mixtures. For PEPU interfaces, the extent of hydrogen bonding at the surface is the dominant contributor to the measured forces. In the case of DNB-phenylglycine and DNB-leucine, CFM measurements of the chiral self-selectivity in 2-propanol demonstrate that chiral discrimination is present in both systems, but larger forces are observed for DNB-phenylglycine, consistent with the molecular dynamics study that shows much weaker solvent interactions with this species. / Thesis (Ph.D, Chemistry) -- Queen's University, 2008-08-14 11:26:37.436

Darbo tikslas yra ištirti etaloninių vanadžio pentoksido ir dioksido Rentgeno fotoelektronų spektrus siekiant nustatyti cheminį poslinkį tarp oksidų V 2p spektrų smailių. Darbe išsamiai aprašytos vanadžio dioksido ir prntoksido struktūros, oksidų savybės, Rentgeno fotoelektronų spektroskopijos metodo pagrindai bei V2O5 ir VO2 Rentgeno fotoelektronų spektrų ypatumai. Aprašyti atliktų eksperimentų metodai. Pateikti eksperimentų ir literatūrinės duomenų bazės analizės rezultatai. Atliktas darbas leido nustatyti sekančius faktus: cheminis poslinkis tarp vanadžio dioksido ir pentoksido etaloninių bandinių Rentgeno fotoelektronų spektrų V 2p3/2 smailių lygus 0.7 eV matuojant spektrus spektrometru XSAM 800 (Kratos Analytical, Anglija); literatūrinių duomenų analizę parodė, kad tikimiausia cheminio poslinkio vertė tarp V 2p3/2 smailių įvairiuose vanadžio junginiuose lygi 1.1 eV; skirtumas tarp eksperimentiškai gautos cheminio poslinkio vertės ir analogiško dydžio gauto iš literatūrinių duomenų analizės sąlygotas tuo, kad buvo matuojami gryni VO2 ir V2O5 bandiniai, o analizei buvo naudojama duomenų visumą apie įvairius vanadžio junginius. / The main aim of the presented work was to investigate the chemical shift between XPS V 2p peaks of standard V2O5 and VO2 samples. The structure and physical properties of vanadium dioxide and pentoxide, X-ray photoelectron spectroscopy basis and some singularities of these oxides XPS spectra are presented. The experimental methods, the results of experiments and the literature analysis results are described. The executed work has allowed establishing following facts: the chemical shift between vanadium dioxide and pentoxide standard samples XPS V 2p peaks is equal to 0.7 eV; the analysis of the literature base shows that this shift for various vanadium compounds is 1.1 eV; the difference between measured chemical shift and chemical shift value established from literature analysis is caused because XPS spectra of pure oxides samples was measured in present work and the analysis of the literature base was performed for various vanadium compounds.

No description available.

In the present thesis the electronic properties of two organic molecules were studied by means of density functional theory (DFT) in connection to their possible applications in organic photovoltaics and molecular spintronics respectively. The first analysed system is the C60 derivative PCBM extensively used in polymer solar cells for the charge separation process. Since fullerenes have been shown to undergo modifications as a result of light exposure, investigating their electronic structure is the first step in elucidating the photodegradation process. The electronic excitations from core levels to unoccupied molecular orbitals reveal not only the empty level structure of the molecule, but provide additional information related to the chemical bonds involving a specific atom type. In this way, they represent a means of determining the chemical changes that the molecule might withstand. The electronic transitions from carbon 1s core levels to unoccupied states are explained for the unmodified PCBM by a joint theoretical (DFT) and experimental study using the near edge x-ray absorption fine structure (NEXAFS) spectroscopy. The second investigated system is the transition metal phthalocyanine with a manganese atom as the metal center. Manganese phthalocyanine (MnPc) is a single molecular magnet in which the spin switch process can be triggered by various methods. It has been shown, for instance, that the adsorption of hydrogen to the Mn center changes the spin state of the molecule from 3/2 to 1. More interestingly, the process is reversible and can be controlled, opening up the possibility of using MnPc as a quantum bit in magnetic memory devices. Up to this date, the d orbital occupation in MnPc has been under a long debate, both theoretical and experimental studies revealing different configurations. In this thesis the electronic structure of the phthalocyanine is thoroughly analysed by means of DFT and the calculated results are compared to photoelectron spectroscopy measurements. The combination of theoretical and experimental tools reveals that in gas phase at high temepratures the molecule exhibits a mixed electronic configuration. In this light, the possible control of the specific electronic state of the central metal represents an interesting prospect for molecular spintronics.

The current thesis presents fundamental studies of phthalocyanines (Pcs), a group of organic macro-cycle molecules. The use of phthalocyanine molecular films in devices with a variety of possible technological applications has been the reason of the many studies dedicated to such molecules during the last decades. Core and valence photoelectron spectroscopies (PES), X-ray absorption spectroscopy (XAS) and scanning tunneling microscopy (STM) techniques are used to study phthalocyanine molecules in gas phase and adsorbed on gold (111) and silicon Si(100)-2x1 substrates. Density functional theory (DFT) is used to obtain further insights in the electronic structure of the phthalocyanines. The aim of our studies is to get a deeper understanding into the molecule-molecule and molecule-substrate interactions, a fundamental requirement for improving the devices based on such molecular materials. Gas phase PES and XAS studies and single molecule DFT calculations are performed on the valence band (VB) of iron phthalocyanine (FePc), manganese phthalocyanine (MnPc) and metal-free phthalocyanine (H2Pc). The VB simulations have shown how the metal atom of the Pc influences the inner valence states of the molecules. The HOMO of the H2Pc and FePc is formed by mostly C2p states, whereas the HOMO of MnPc has mainly Mn3d character. PES studies of H2Pc on Au(111) have revealed the influence of the surface on the adsorption of the monolayer. XAS studies indicate formation of ordered monolayer with the Pc ligands parallel to the surface and the change of the molecular tilt angle with increasing thicknesses. For LuPc2 adsorbed on Au(111), STM study demonstrates a formation of bilayer instead of a monolayer. A comparison between the results of LuPc2 adsorbed on pristine or passivated Si(100)-2x1 confirmes the different reactivities of these surfaces: LuPc2 retains many molecular-like characters, when adsorbed on the innert passivated Si. Instead, on the more reactive pristine Si surface, the spectroscopic results have indicated a more significant interaction, possible hybridization and charge redistribution between the molecules and the surface. Moreover, STM images show a modification of the geometrical shape of the molecules, which are proposed to adsorb in two different geometries on the pristine Si surface.