High resolution molecular spectroscopic techniques are useful tools to accurately probe energy differences between quantum states of molecules. These energy levels are inherently dependent on the underlying potential functions, which ultimately govern the structures and dynamics of molecules. Thus, the detailed characterization of potential energy profiles through molecular spectroscopy provides important information about molecular properties. Given the increased structural and dynamic complexity of large molecules, small compounds serve as excellent prototypes to establish quantum mechanical models that accurately characterize quantum states and ultimately potential energy functions of various molecular classes. This thesis describes the use of rotational and rovibrational spectroscopy to probe one such class: four-membered heterocycles. Rotationally-resolved vibrational spectra of four-membered rings including β-propiolactone (c-C3H4O2), 3-oxetanone (c-C3H4O2), azetidine (c-C3H6N) and silacyclobutane (c-C3H8Si) were recorded below 1200 cm-1 using a Fourier transform infrared spectrometer (FTIR) with synchrotron light at the far infrared beamline of the Canadian Light Source (CLS). Additionally, Fourier transform microwave (FTMW) spectroscopy was used to study the pure rotational spectra of β-propiolactone and silacyclobutane for the first time. This allowed the accurate characterization of the ground vibrational state and molecular structure in support of the rovibrational analysis. The far infrared vibrational modes of these four molecules were analyzed individually initially and followed by a global fit of all observed transitions of each molecule. Unique spectroscopic signatures arising from Coriolis coupling(β-propiolactone, 3-oxetanone), tunneling motions (azetidine, silacyclobutane) and the large amplitude ring puckering vibration (3-oxetanone, azetidine, silacyclobutane) were revealed and treated. The resultant Hamiltonian models used for each molecule account for the observed spectra as the spectroscopic constants are consistent across the ground state and all vibrationally excited states studied. Collectively, these studies have provided a highly effective working protocol for the treatment of high resolution rovibrational data to model the dynamic behaviour of real molecules.

This thesis addresses one of the major outstanding problems in the study of self-assembled InAs quantum dots (QDs): their physical profile after deposition of a capping layer and post-growth processing. The optical properties of QDs depend critically on the shape, composition and strain profile, yet these parameters are inaccessible to most experimental techniques once the dots are buried. Data from various x-ray scattering experiments are presented here, along with a novel approach to simulating diffuse scattering using an atomistic model based on Keating energy minimisation. The size and position of the diffuse scattering on the low-Q side of the Bragg peak, which are strongly influenced by the shape and composition of the QDs, has been used to determine that the QDs are truncated pyramids with a diagonal base length of 28 nm, with their edges aligned along the [100] and [010] directions. The composition profile varies from pure InAs at the top to 40-60% InAs at the base. These properties all agree with recent cross-sectional scanning tunnelling microscopy (X-STM) measurements by Bruls et al. It was shown that post-growth annealing causes a reduction in the In content of the QDs, primarily by diffusion from the base of the dot into the wetting layer. Grazing incidence small angle x-ray scattering (GISAXS) measurements have been made from samples of QDs produced with varying growth interruptions (GI) before deposition of the capping layer. The QDs were found to be highly diffuse. After a GI, the dots have been shown to change shape anisotropically, with two facets becoming sharper. An investigation of the use of resonant scattering to study buried QDs has shown that the method of contrast variation is of limited use for enhancing the measurement of diffuse features away from the Bragg peak. It is unsuitable for the study of buried nanostructures.

No description available.

Techn. Universiẗat, Diss., 2006--Darmstadt.

Darmstadt, Techn. Universiẗat, Diss., 2007. / Dateien im PDF-Format.

Thesis (Ph. D.)--University of Hong Kong, 1990.

Orientador: Eduardo Granado Monteiro da Silva / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-19T18:24:03Z (GMT). No. of bitstreams: 1 Marcondes_RafaelJoseFranca_M.pdf: 4781078 bytes, checksum: 963ca375d793021d73e27eaf311966c2 (MD5) Previous issue date: 2012 / Resumo: Um novo anel de armazenamento de elétrons está sendo projetado para a produção de luz síncrotron de alto brilho no Laboratório Nacional de Luz Síncrotron (LNLS), em Campinas. Para atingir um alto brilho, requer-se uma forte focalização do feixe, levando a fortes não-linearidades dos campos magnéticos, o que limita a região de estabilidade do movimento dos elétrons. Neste trabalho, estudamos a dinâmica destas partículas no anel e aplicamos métodos para a otimização da abertura dinâmica / Abstract: A new electron storage ring, Sirius, is being designed for the production of high brightness synchrotron light at the Brazilian Synchrotron Light Laboratory (LNLS), in Campinas. To achieve high brightness, strong focusing of the beam is required, leading to strong non-linearities in the magnetic elds, which limit the region of stable motion of the electrons. In this work we study the dynamics of these particles in the ring and apply methods for the optimisation of the dynamic aperture / Mestrado / Mestre em Física

Particulate and dissolved forms of arsenic and heavy metals are released from legacy mine tailings, particularly in (semi-) arid environments where tailings remain barren of vegetation and therefore highly susceptible to erosion. This leads to contamination of adjacent ecosystems and increased risk to public health. Establishment of a vegetative cap using amendments, such as composted organic matter to enhance plant growth, may be employed to reduce both physical erosion and leaching, but the impacts of such practices on molecular-scale mechanisms controlling metal(loid) speciation and lability remain poorly understood. Here we report on subsurface biogeochemical transformations of metal(loid)s in a phytostabilization field study at a Superfund site in Arizona, USA, where a legacy pyritic tailings (4,000 mg kg^-1 As, 2,438 mg kg^-1 Pb, 6,142 mg kg^-1 Zn, 13.25% Fe, and 11.71% S, averages for the top 0.5 m) has undergone oxidation in the top 1 m. Tailings were amended in the top 20 cm with 10%, 15%, and 20% composted organic matter by mass and seeded with native halotolerant plant species. All field treatments and the uncomposted control received irrigation of 0.36 ± 0.03 mm y^-1 in addition to 0.25 ± 0.16 mm y^-1 of precipitation, resulting in water input of 144% the annual precipitation rate. The field trial incorporated four annual samplings from 2010 – 2013. Sampling consisted of a single core of 90 cm in length and 2.54 cm in diameter collected from each field plot that was subsequently sectioned into 20 cm depth increments for analysis by synchrotron Fe and As X-ray absorption spectroscopy (XAS) coupled with quantitative chemical extraction methods. Subsurface stabilization of arsenic by Prosopis juliflora (mesquite) was investigated by bulk and micro synchrotron XAS and multiple-energy microscale fluorescence mapping combined with chemical digestion of plant samples following 1, 2, and 3 months of growth in greenhouse microcosms as well as 14 and 36 months of growth at the field site. Results indicate persistence of oxidizing conditions following compost amendment in surface tailings despite addition of organic matter, development of heterotrophic microbial communities and irrigation of a poorly draining medium. Compost amendment of 20% corresponded with evidence of higher oxidative pyrite weathering activity at 40-60 cm depth during phytostabilization compared to treatments of 0% or 10% compost for which the highest oxidative pyrite weathering activity was observed closer to the surface at 20-40 cm depth.. Despite observed downward transport of As, Fe, Zn, Mn, Pb, Ni, Cu, Cr, V, and Co during phytostabilization, ≥ 75% of total As was found to be attenuated by ferrihydrite in surface depths. Attenuation of Mn, Co, and Ni was observed below 40 depth by tailings receiving compost amendment relative to the irrigated control. Root associated As(V) was immobilized on the root epidermis bound to ferric sulfate precipitates and within root vacuoles as trivalent As(III)-thiol complexes. Rhizoplane associated ferric sulfate phases were dissimilar from the bulk tailings mineralogy shown by XAS and exhibited a high capacity to scavenge As(V) with As:Fe ratios 2x higher than the compost amended growth medium, indicating a root surface mechanism for their formation or accumulation. Results indicate that arsenate attenuation in semi-arid mine tailings during phytostabilization greatly depends on the presence of high concentrations of Fe(III) (oxyhydr)oxide minerals with a high capacity for arsenic adsorption.

Titanium dioxide (TiO2) is an abundant, inexpensive and non-toxic material that is most commonly used as a white pigment in paints. Since the discovery by Fujishima and Honda in 1972 that water splits into hydrogen and oxygen gas at the surface of TiO2 on exposure to sunlight, there has been a massive research effort into understanding and improving the photoactivity of TiO2. One aspect of this is the characterisation of so-called ‘model’ surfaces, i.e. very large single crystal faces with low levels of contamination at ultra high vacuum (UHV) pressures, allowing the study of a single structure with a minimum of unknown variables effecting experimental results. Two techniques that are used to probe surface structure, amongst many, are Surface X-ray Diffraction (SXRD) and Photoelectron Spectroscopy (PES). SXRD allows quantitative determination of surface structure with high precision, and PES reveals surface chemical composition. In the context of this thesis both of these techniques were exploited at synchrotron radiation sources, which produce light of high brightness. In addition, the development of routines for extraction of SXRD data from 2D detectors to allow SXRD analysis is described. SXRD is employed to probe the structure of anatase-TiO2(101) both in UHV and following immersion in water vapour. The optimum UHV structure is largely in agreement with that previously predicted computationally, although there are some discrepancies in terms of atomic displacements. Water immersion leads to a H2O/OH terminated surface. The surface structure of a rutile-TiO2(110)(1x1) surface, that had been prepared under non-UHV conditions, using a wet chemical preparation technique, is also determined with SXRD. The studied surface, which was highly hydrophilic, has a similar substrate termination to UHV-prepared rutile-TiO2(110)(1x1) but with adsorbed surface H2O/OH species. Finally, PES is used to gain insight into the O1s signature of surface bridging oxygens on rutile-TiO2(110), as well as those (if any) of oxygen adatoms. Concerning bridging oxygens, it is demonstrated that there is no discernable shift in the O1s core level for these atoms away from the bulk oxide peak. Regarding oxygen adatoms, no conclusive evidence of a distinct emission signal in the O1s core level or valence band spectra can be discerned, due to interference from carbon contamination.

L’histologie virtuelle est un domaine qui suscite un intérêt de recherche croissant. Nous nous intéressons à une de ces techniques en particulier via l’imagerie de contraste de phase par rayonnement synchrotron. Cette imagerie nous permet d’observer des cerveaux de souris intacts avec une résolution spatiale de 8µm isotropique, soit une résolution similaire à celle d’une histologie optique classique mais sans endommager les tissus par des colorations ou des marquages spécifiques. Ces travaux de thèse sont organisés autour de trois grands axes. Un premier axe présente l’instrumentation photonique qui permet l’obtention du contraste de phase et le paramétrage original qui est proposé pour l’acquisition d’échantillons biologiques de composition hétérogène. Un second axe présente différents traitements d’images développés pour des tâches informationnelles précises telles que l’optimisation de la visualisation, la détection d’agrégats cellulaires et la tractographie de structures fibreuses. Enfin, une application biomédicale de ces traitements est proposée via la détection et la quantification de nanoparticules d’oxyde de fer dans un modèle expérimental d’accident vasculaire cérébral. / Virtual histology is a field of investigation with growing interest in the commmunity of bioimage analysis. We focus on one of these techniques with the phase contrast tomography using synchrotron radiation. This technique allows us to visualize mice brains with no impact and with a spatial resolution of 8µm isotropically, which is a resolution similar to the one obtained with classic optical histology but without damaging samples with specific dyeing. This thesis is organized along three main axes. The first one presents photonic instrumentation which gives us access to the phase information and the original setting of a reconstruction parameter for the acquisition of biological heterogeneous samples. A second axis shows several image processing developed in order to address different informational tasks such as visual optimization, cellular aggregates detection or fiber tractography. Eventually, a biomedical application of these process is proposed by adressing detection and quantification of iron oxide nanoparticles in an experimental model of stroke.