Dissertations / Theses on the topic 'X-ray scattering'
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1
Klos, Richard A. "Scattering from X-ray mirrors." Thesis, University of Leicester, 1987. http://hdl.handle.net/2381/35710.
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Scattering from X-ray Mirrors deals with the the phenomena observed when x-rays are reflected from high quality mirror surfaces at grazing incidence. The presence of micro- irregularities in the reflecting surface causes power to be deviated away from the specular direction and into the wings of the angular distribution of radiation. Both theoretical and experimental investigations are presented. The two principal theories of the scattering of electromagnetic radiation are reviewed and are shown to produce identical results in the smooth surface limit. The scalar theory is further developed so as to be applicable to a scattering surface which can be described by an arbitrary surface height distribution function for any surface autocovariance function. The theoretical advances reported suggest a means by which the surface height distribution statistics of mirror surfaces might be derived from experimental scattering measurements. The experimental work in the thesis deals with a scattering experiment designed to test these theoretical developments. The development work involved in the construction of the Variable Angle Scattering Experiment (VASE) is presented and the anomalous results obtained from scattering measurements from two test flat x-ray mirrors are discussed. A shadowing model is devised to account for the anomalous results from the VASE. The shadowing model is then shown to be in good agreement with the VASE data and with data from other scattering experiments. The shadowing model, which provides a means of measuring the properties of pure mirror surfaces, is further developed to enable measurements of surface structure on mirrors which have become specked with small sparse contaminant features, thus allowing highly sensitive estimates of contaminant density and height to be made.
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Spencer, Philip David. "Charge and magnetic X-ray scattering." Thesis, Durham University, 2004. http://etheses.dur.ac.uk/2994/.
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The hole doped transition metal oxides show remarkable properties that are related to the influence of charge and spin correlations. In this thesis charge correlations in hole doped manganite and nickelate systems are smdied using soft (˂2 keV), normal (10 keV) and high energy x-ray scattering (100 keV).The charge and J aim-Teller (JT) order is studied in the bi-layer manganite La(_2)-(_2r) Sr(_1)+(_2x)Mn(_2)O(_7) for x = 0.5, 0.55 and 0.60 using high energy x-ray scattering. In the x = 0.55 sample the charge ordered state existed in the same checkerboard pattern as observed in the x = 0.5 sample with no change in behaviour. However, in the x = 0.6 doped sample the charge ordered state entered a new regime characterised by incommensurate JT and charge order. The magnitude of the incommensurability was inversely proportional to the intensity of the JT and charge peaks. High resolution x-ray measurements of the charge stripe order in the La(_2-x)Sr(_x)NiO(_4) system in the doping range 0.20 ≤ x ≤ 0.50 are presented. As the doping was moved away in either direction from the commensurate x = 0.33 the charge stripes changed from a highly correlated state to an increasingly disordered charge glass state. At the commensurate 0.5 composition there was no increase in the intensity or correlation of the charge order despite a significantly higher transition temperature than in the lower doped compositions. Finally the first measurements of the orbital order in La(_0.5)Sr(_1.5) MnO(_4) using soft x-ray scattering at the manganese L edges are presented. The measurements directly probe the orbital order unlike the previously reported measurements at the manganese K-edge. Energy scans were carried out on the orbital order and compared with theoretical predictions. From this it was determined that both the Jahn-Teller distortions and direct orbital ordering contribute to the observed scattering.
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McSherry, Declan J. "X-ray scattering from dense plasmas." Thesis, Queen's University Belfast, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394619.
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Froud, Christopher Andrew. "Designing a nanoscale X-ray source : towards single molecule X-ray scattering." Thesis, University of Southampton, 2007. https://eprints.soton.ac.uk/52042/.
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This thesis describes the design and construction of a femtosecond X-ray source based on high harmonic generation in an argon filled hollow capillary waveguide. The system has demonstrated excellent efficiency at generating harmonics in the range 20-50 eV and is tuneable by exploiting the ionization-induced blue-shift that occurs in the waveguide. The X-ray source is designed for X-ray scattering experiments, which will ultimately allow the imaging of single biomolecules. Such experiments will require an intense, focused X-ray beam. Towards this aim, this thesis demonstrates focusing techniques based on tapered capillary optics, including a model that was developed to understand their behaviour.
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Feldkamp, Jan Moritz. "Scanning Small-Angle X-Ray Scattering Tomography." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-24925.
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The techniques of small-angle x-ray scattering (SAXS) and grazing-incidence small-angle x-ray scattering (GISAXS) have successfully been used for many years in the analysis of nanostructures in non-crystalline samples, e.g., polymers, metallic alloys, ceramics, and glasses. In many specimens, however, the nanostructure is not distributed homogeneously, but instead varies as a function of position in the sample. Conventional SAXS or GISAXS measurements on such heterogeneous samples merely yield an averaged scattering pattern of all the different structures present along the x-ray beam path. In this thesis, scanning tomography is combined with SAXS and GISAXS, revealing the individual local scattering cross section at each position on a virtual section through the sample. The technique thereby offers unique analytical possibilities in heterogeneous specimens. A brief review of the physics of x rays and x-ray scattering is given, before the methods of tomographic SAXS and GISAXS are introduced. Experimental requirements and limitations of both methods are discussed, including aspects of sampling, local rotational invariance and x-ray beam coherence. Experiments performed at the beamline BW4 at HASYLAB at DESY, Hamburg, Germany are described, illustrating the capabilities of the method. Finally, an outlook on possible future developments in tomographic small-angle x-ray scattering is givenDie Methoden der Röntgenkleinwinkelstreuung (SAXS) und Röntgenkleinwinkelstreuung unter streifendem Einfall (GISAXS) werden seit vielen Jahren erfolgreich eingesetzt zur Analyse von Nanostrukturen in nicht-kristallinen Proben, z.B. Polymeren, metallischen Legierungen, Keramiken und Gläsern. In vielen Proben ist die Nanostruktur allerdings nicht homogen verteilt, sondern variiert als Funktion des Ortes in der Probe. Konventionelle SAXS- oder GISAXS-Messungen an solch heterogenen Proben liefern lediglich ein über alle unterschiedlichen Strukturen entlang des Röntgenstrahls gemitteltes Streubild. In dieser Arbeit wird Rastertomographie mit SAXS und GISAXS kombiniert und so der lokale Streuquerschnitt an jedem Ort auf einem virtuellen Schnitt durch die Probe gewonnen. Diese Technik bietet so einzigartige Analysemöglichkeiten von heterogenen Proben. Es wird zunächst ein kurzer Überblick über die Physik der Röntgenstrahlung und Röntgenstreuung gegeben, bevor die Methoden der SAXS- und GISAXS-Tomographie eingeführt werden. Die experimentellen Anforderungen und Grenzen beider Methoden werden besprochen, wobei Aspekte der Abtastung, der lokalen Rotationsinvarianz und der Kohärenz im Röntgenstrahl eine Rolle spielen. Experimente, die an der Messstrecke BW4 am HASYLAB bei DESY, Hamburg, durchgeführt wurden, werden beschrieben, um die Möglichkeiten der Methode zu illustrieren. Schließlich wird ein Ausblick auf mögliche zukünftige Entwicklungen der Kleinwinkelstreutomographie gegeben
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Sun, Yu-Ping. "Spontaneous and stimulated X-ray Raman scattering." Doctoral thesis, KTH, Teoretisk kemi (stängd 20110512), 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-32859.
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The present thesis is devoted to theoretical studies of resonant X-ray scattering and propagation of strong X-ray pulses. In the first part of the thesis the nuclear dynamics of different molecules is studied using resonant X-ray Raman and resonant Auger scattering techniques. We show that the shortening of the scattering duration by the detuning results in a purification of the Raman spectra from overtones and soft vibrational modes. The simulations are in a good agreement with measurements, performed at the MAX-II and the Swiss Light Source with vibrational resolution. We explain why the scattering to the ground state nicely displays the vibrational structure of liquid acetone in contrast to excited final state. Theory of resonant X-ray scattering by liquids is developed. We show that, contrary to aqueous acetone, the environmental broadening in pure liquid acetone is twice smaller than the broadening by soft vibrational modes significantly populated at room temperature. Similar to acetone, the "elastic" band of X-ray Raman spectra of molecular oxygen is strongly affected by the Thomson scattering. The Raman spectrum demonstrates spatial quantum beats caused by two interfering wave packets with different momenta as the oxygen atoms separate. It is found that the vibrational scattering anisotropy caused by the interference of the "inelastic" Thomson and resonant scattering channels in O2. A new spin selection rule is established in inelastic X-ray Raman spectra of O2. It is shown that the breakdown of the symmetry selection rule based on the parity of the core hole, as the core hole and excited electron swap parity. Multimode calculations explain the two thresholds of formation of the resonant Auger spectra of the ethene molecule by the double-edge structure of absorption spectrum caused by the out-of- and in-plane modes. We predict the rotational Doppler effect and related broadening of X-ray photoelectron and resonant Auger spectra, which has the same magnitude as its counterpart-the translational Doppler effect. The second part of the thesis explores the interaction of the medium with strong X-ray free-electron laser (XFEL) fields. We perform simulations of nonlinear propagation of femtosecond XFEL pulses in atomic vapors by solving coupled Maxwell's and density matrix equations. We show that self-seeded stimulated X-ray Raman scattering strongly influences the temporal and spectral structure of the XFEL pulse. The generation of Stokes and four-wave mixing fields starts from the seed field created during pulse propagation due to the formation of extensive ringing pattern with long spectral tail. We demonstrate a compression into the attosecond region and a slowdown of the XFEL pulse up to two orders of magnitude. In the course of pulse propagation, the Auger yield is strongly suppressed due to the competitive channel of stimulated emission. We predict a strong X-ray fluorescence from the two-core-hole states of Ne created in the course of the two-photon X-ray absorption.QC 20110426
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Busono, Pratondo. "Combined transmission and scattering x-ray tomography." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0025/NQ38344.pdf.
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Su, Tsueu-Ju. "Neutron and X-ray scattering from interfaces." Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319060.
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White, Steven Jonathan. "X-ray scattering from warm dense matter." Thesis, Queen's University Belfast, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603562.
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Experimentally observed x-ray scattering from warm dense samples of iron has been achieved for the first time. This work was carried out at the Vulcan laser facility to investigate the properties of iron under conditions typical of warm dense matter, similar to those found at the boundary between the Earth's inner and outer cores. Suitable samples of iron were generated using the method of direct drive, laser produced shock compression. This was achieved, using intensities of 1033 W/cm2 with frequency doubled (2w at 527 nm) = 1 ns laser pulses, incident upon 7um iron foil targets, coated in 6um of parolee-N plastic. The iron samples were probed using a helium like titanium line source spectrum (ls2-1s2p , 4.75 Kev, 1% D.'A/A ). Spectrally and angularly resolved elastic scattering; collected using 3 HOPG (2d = 6.708 Angstroms) Bragg crystal spectrometers operating In Von Hams geometry, was observed for scattering angles between 30° to 90°, and for a range of plasma conditions (p::::: (2 to 14) g/cc, The (0.2 to 2) eV; and Z=2 to 5). The shock speed has been evaluated by optical streak pyrometer, and comparison with hydrodynamic simulations established that the iron evolves to a molten state at several 100s GA pressure. The experimental design, analysis, and calculation of scattering cross sections have been described in detail. The observed cross sections have been compared with a simple one component plasma model, which highlighted the importance of screening of the inter-ionic potential to the predicted scattering signal. The method of accounting for the long probe duration (- Ins) when processing the results of hydrodynamic simulations, to allow comparison to, and validation of more sophisticated models of scattering, has also been discussed.
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Rawle, Jonathan Leonard. "X-ray scattering from InAs quantum dots." Thesis, University of Leicester, 2005. http://hdl.handle.net/2381/27586.
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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.
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Hase, Thomas Paul Anselm. "X-ray scattering from magnetic metallic multilayers." Thesis, Durham University, 1998. http://etheses.dur.ac.uk/4652/.
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Study of structure and interface morphology of magnetic thin films is crucial in obtaining a better understanding of the coupling mechanisms in such systems. In this thesis various x-ray scattering techniques are applied to a series of Co/Cr trilayers, Cu/Co multilayers and spin valve structures. It is demonstrated that modifications to the distorted wave Born approximation allow the modelling of grazing incidence diffuse scatter originating from graded systems such as Co/Cr. Grazing incidence scattering techniques are also employed to investigate the out of plane correlations of lateral roughness in Cu/Co multilayers, as well as in miscible trilayer structures. The use of soft x-rays in the investigation of 3d transition metal multilayers is also presented. Such experiments are sensitive to the component of magnetisation aligned with the direction of the incident beam. In a series of magnetisation experiments, the dependence of the x-ray scatter sensitive to this component of magnetisation are analysed. For the first time evidenced is found for correlated magnetic roughness, which has lateral correlation lengths far greater than the structural roughness length scales. This magnetic roughness is measured in detail, and the correlation length is found to vary with applied field direction. Grazing incidence x-ray fluorescence is applied to two spin valve structures. These experiments provide a direct measure of buried layer thicknesses which is not possible by other x-ray scattering techniques. This novel method for the determination of the copper layer thickness in spin valves shows the versatility of non-destructive x-ray methods for the characterisation of magnetic metallic multilayers.
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Moore, Caroline Dale. "X-ray scattering studies of compound semiconductors." Thesis, Durham University, 1997. http://etheses.dur.ac.uk/4755/.
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In this thesis, techniques of high resolution x-ray diffraction, topography and grazing incidence reflectivity have been employed in order to gain information on compound semiconductors. A recent growth technique. Vertical Gradient Freeze (VGF), has been investigated for 2" InP wafers, and been found to produce virtually dislocation- free crystals. In the one wafer where dislocations have been imaged, they have a density of ~200cm(^-2), with Burgers vectors lying in the plane of the wafer. This is in contrast to topographs of Liquid Encapsulated Czochralski (LEG) InP, where a dislocation density of up to 6.10'(^4)cm(^-2) was observed at the wafer periphery. No growth striations were observed in VGF samples, implying a planar solid-melt interface. VGF GaAs wafers are seen to be virtually dislocation free when Si doped, have dislocation densities of 900cm(^-2) when undoped and 1200cm(^-2) when Zn doped. Triple axis diffraction measurements showed a variation in tilts between/samples, but no strain variation. The tilt variation was attributed to the polishing process. Asymmetric scans showed a variation in strain at high tilts. These data have been used to form a model for the crystal surface: mosaic blocks of perfect crystal surrounded by low angle boundaries consisting of rows of edge dislocations. During the polishing process, these blocks are physically rotated, evidence for which is supplied from analysis of the specular part of reflectivity scans. Specular and diffuse reflectivity scans on InP substrates have been simulated using the Distorted Wave Born Approximation (DWBA). In all cases a 30Å thick oxide layer was identified on the sample surface. In order to obtain a good simulation for transverse scans at two values of q(_z), it was necessary to include a grading in electron density at the top surface. Epitaxial layers of Hg(_1-x)Mn(_x)Te (MMT) grown by the Interdiffused Multilayer Process (IMP) on GaAs with a CdTe buffer layer have been characterised using double and triple axis diffraction. Although reasonable compositional uniformity was observed across the wafers (from 0.3%mm(^-1)), dynamical simulations of pseudo-triple axis scans showed a grading in composition with depth. It was observed that the crystalline perfection deteriorated with increased Mn fraction. The MMT and CdTe layers were almost fully relaxed, and were found to have dislocation densities of l0(^7)-l0(^9)cm(^-2). In one sample the presence of zinc blende MnTe was established using double axis diffraction. Finally, the high intensity of the European Synchrotron Radiation Facility (ESRF) has been exploited in order to topograph highly absorbing materials. The effect of heater failure in the growth of GaAs in space has been shown to produce high levels of strain and twinning. It has also been shown topographically that contact with the crucible during the growth of GaInSb from the melt leads to increased strain, so de-wetting phenomena improve crystalline growth.
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Burton, Nicholas. "X-ray magnetic scattering from neodymium metal." Thesis, University of Birmingham, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396458.
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Garcia, Saiz M. E. "X-Ray Scattering From Warm Dense Matter." Thesis, Queen's University Belfast, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501262.
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Norwell, George A. "X-ray scattering by cosmic dust grains." Thesis, Keele University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293990.
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Schmising, Clemens von Korff. "Femtosecond X-ray scattering in condensed matter." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2008. http://dx.doi.org/10.18452/15871.
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Diese Arbeit untersucht die vielfältigen Wechselwirkungen zwischen elektronischen und strukturellen Eigenschaften in Perovskit-Oxiden und in einem molekularen Kristall. Optische Anregung mit ultrakurzen Lichtimpulsen verändert die elektronische Struktur und die Dynamik der damit verbundenen reversiblen Gitterveränderung wird mit zeitaufgelöster Femtosekunden Röntgenbeugung direkt aufgezeichnet. Eine Nanostruktur aus metallischen und ferromagnetischen Strontium Ruthenat (SRO) und dielektrischen Strontium Titanat Schichten dient als Modellsystem, um optisch induzierten Druck auf einer subpikosekunden Zeitskala zu untersuchen. In der ferromagnetischen Phase zeigen phononischer und magnetostriktiver Druck eine vergleichbare ultraschnelle Dynamik und eine ähnliche Größe unterschiedlichen Vorzeichens. Die Amplitude des magnetischen Drucks folgt dem Quadrat der temperaturabhängigen Magnetisierung. In einem weiteren Doppelschichtsystem komprimiert der sich ultraschnell aufbauende phononische Druck in SRO benachbarte ferroelektrische Blei Zirkonat Titanat Schichten. Dies reduziert die tetragonale Verzerrung von bis zu 2 Prozent innerhalb 1.5 Pikosekunden und koppelt an die ferroelektrische "weiche Mode", beziehungsweise an die Ionenverschiebung innerhalb der Einheitszelle. Damit verbunden wird die makroskopische Polarisation bis zu 100 Prozent reduziert; aufgrund der Anharmonizität der Kopplung mit einer Verzögerung von 500 Femtosekunden. Femtosekunden Photoanregung von Chromophoren in einem molekularen Kristall induziert eine Änderung des Diopolmomentes durch intramolekularen Ladungstransfer. Die Änderung der gestreuten Röntgenintensität weist auf eine Molekül-Rotationsbewegung in der Umgebung angeregte Dipole hin, welche der 10 Pikosekunden Dynamik des Ladungstransfer folgt. Die transienten Röntgenstreusignale werden vollständig von der kollektiven Solvatation bestimmt und verdecken lokale, intramolekulare Strukturänderungen.This thesis investigates the manifold couplings between electronic and structural properties in crystalline Perovskite oxides and a polar molecular crystal. Ultrashort optical excitation changes the electronic structure and the dynamics of the connected reversible lattice rearrangement is imaged in real time by femtosecond X-ray scattering experiments. An epitaxially grown superlattice consisting of alternating nanolayers of metallic and ferromagnetic strontium ruthenate (SRO) and dielectric strontium titanate serves as a model system to study optically generated stress. In the ferromagnetic phase, phonon-mediated and magnetostrictive stress in SRO display similar sub-picosecond dynamics, similar strengths but opposite sign and different excitation spectra. The amplitude of the magnetic component follows the temperature dependent magnetization square, whereas the strength of phononic stress is determined by the amount of deposited energy only. The ultrafast, phonon-mediated stress in SRO compresses ferroelectric nanolayers of lead zirconate titanate in a further superlattice system. This change of tetragonal distortion of the ferroelectric layer reaches up to 2 percent within 1.5 picoseconds and couples to the ferroelectric soft mode, or ion displacement within the unit cell. As a result, the macroscopic polarization is reduced by up to 100 percent with a 500 femtosecond delay that is due to final elongation time of the two anharmonically coupled modes. Femtosecond photoexcitation of organic chromophores in a molecular, polar crystal induces strong changes of the electronic dipole moment via intramolecular charge transfer. Ultrafast changes of transmitted X-ray intensity evidence an angular rotation of molecules around excited dipoles following the 10 picosecond kinetics of the charge transfer reaction. Transient X-ray scattering is governed by solvation, masking changes of the chromophore''s molecular structure.
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Grabis, Johannes. "Soft X-ray resonant scattering from magnetic heterostructures." [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=974077038.
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Heitner, Gabriele Heike. "Multiple scattering for diffraction enhanced X-ray imaging." [S.l. : s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=976522632.
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Salek, Pawel. "Wave packet theory of resonant X-ray scattering." Doctoral thesis, KTH, Bioteknologi, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3188.
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Warren, Andrew. "X-ray Scattering Investigations of Metallic Thin Films." Doctoral diss., University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5721.
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Nanometric thin films are used widely throughout various industries and for various applications. Metallic thin films, specifically, are relied upon extensively in the microelectronics industry, among others. For example, alloy thin films are being investigated for CMOS applications, tungsten films find uses as contacts and diffusion barriers, and copper is used often as interconnect material. Appropriate metrology methods must therefore be used to characterize the physical properties of these films. X-ray scattering experiments are well suited for the investigation of nano-scaled systems, and are the focus of this doctoral dissertation. Emphasis is placed on (1) phase identification of polycrystalline thin films, (2) the evaluation of the grain size and microstrain of metallic thin films by line profile analysis, and (3) the study of morphological evolution in solid/solid interfaces. To illustrate the continued relevance of x-ray diffraction for phase identification of simple binary alloy systems, Pt-Ru thin films, spanning the compositional range from pure Pt to pure Ru were investigated. In these experiments, a meta-stable extension of the HCP phase is observed in which the steepest change in the electronic work function coincides with a rapid change in the c/a ratio of the HCP phase. For grain size and microstrain analysis, established line profile methods are discussed in terms of Cu and W thin film analysis. Grain sizes obtained by x-ray diffraction are compared to transmission electron microscopy based analyses. Significant discrepancies between x-ray and electron microscopy are attributed to sub-grain misorientations arising from dislocation core spreading at the film/substrate interface. A novel "residual" full width half max parameter is introduced for examining the contribution of strain to x-ray peak broadening. The residual width is subsequently used to propose an empirical method of line profile analysis for thin films on substrates. X-ray reflectivity was used to study the evolution of interface roughness with annealing for a series of Cu thin films that were encapsulated in both SiO2 and Ta/SiO2. While all samples follow similar growth dynamics, notable differences in the roughness evolution with high temperature ex-situ annealing were observed. The annealing resulted in a smoothing of only one interface for the SiO2 encapsulated films, while neither interface of the Ta/SiO2 encapsulated films evolved significantly. The fact that only the upper Cu/SiO2 interface evolves is attributed to mechanical pinning of the lower interface to the rigid substrate. The lack of evolution of the Cu/Ta/SiO2 interface is consistent with the lower diffusivity expected of Cu in a Cu/Ta interface as compared to that in a Cu/SiO2 interface. The smoothing of the upper Cu/SiO2 interface qualitatively follows that expected for capillarity driven surface diffusion but with notable quantitative deviation.Ph.D.
Doctorate
Materials Science Engineering
Engineering and Computer Science
Materials Science and Engineering
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Nasedkin, Alexandr. "Tracing Molecular Conformations by X-ray Solution Scattering." Doctoral thesis, Uppsala universitet, Fysikalisk kemi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-230563.
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In the present work the refinement of X-ray data have been used to solve different scientific problems, namely drug localization in the liposome wall, reaction kinetics of the small molecule upon excitation and resolving an ensemble of protein structures at different temperatures. The common approach included collection of X-ray scattering patterns, modelling of the system of interest in atomic level and fitting computed results to experimental data. Employed fitting algorithms varied depends on the application ranging from inverse matrix calculations to the genetic algorithm for complex tasks. Observed results broaden our understanding of investigated systems on molecular level and also lead to development faster, more effective ways to sample atomic structures by X-ray diffusion scattering.
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Lucas, Christopher Andrew. "X-ray scattering studies of surfaces and interfaces." Thesis, University of Edinburgh, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.253861.
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Clarke, John. "X-ray scattering from thin films and interfaces." Thesis, Durham University, 1999. http://etheses.dur.ac.uk/4499/.
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The non-destructive study and characterisation of thin films and their interfaces, on an atomic scale, is a crucially important area of study in many areas of science and technology. In this thesis both high angle and grazing incidence x-ray scattering techniques have been used to study the effect of depositing thin films on surfaces with a periodic roughness, as well as studying the structure of laterally modulated surfaces themselves. High angle diffraction measurements of the out-of-plane size of Co crystallites and the crystalline texture of the Ag lattice, in a series of CoAg granular fihns, has allowed a consistent growth mechanism for the Co grains to be deduced. In grazing incidence scattering studies of this series of thin, granular films it was observed that the diffuse scatter was offset from the specular condition and the position of this offset was seen to vary, sinusoidally, upon rotation of the sample. This led to the conclusion that the growth techniques employed had caused a regular step-bunching of the Si (111) substrate. As step-bunching of surfaces can affect greatly the properties of thin films deposited on them, the ability to characterise the substrate after growth is extremely important. In spin-valves deposited on rough, tiled, silicon oxide substrates, the presence of strong interference fringes in the off-specular scatter demonstrated that vertically conformal roughness dominated the system and this was seen to result in the degradation of the magnetic sensitivity of the samples. Conversely, an enhancement in the photoluminescence from thin polymer films deposited on laterally modulated substrates led to a series of studies being made on such structures. In order to obtain information on the lateral period of such structures, as well as their roughness and thickness, existing scattering theories have been modified and a semi-kinematical code of the coherent scatter has been developed.
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Fulthorpe, Brian David. "X-ray scattering in giant magneto-resistive multilayers." Thesis, Durham University, 1999. http://etheses.dur.ac.uk/4300/.
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The scattering mechanisms responsible for Giant Magneto-Resistance (OMR) in magnetic multilayers are believed to be related to many aspects of the multilayer structure. X-ray scattering techniques provide a powerful method with which to study the bulk and interface morphology in these systems, and are therefore crucial in developing an understanding of the dominant factors influencing the magnitude of the OMR. Reflectivity measurements performed on a series of Co/Cu multilayers, sputter deposited onto etched silicon, reveal no variation in the interface roughness with etching voltage, the thickness of the individual layers also remaining constant. The observed decrease in the OMR cannot, therefore, be attributed to variations in spacer thickness or interfacial spin-independent scattering. Electron and X-ray Diffraction measurements suggest the reduction in GMR is due to a loss of antiferromagnetic coupling associated with a transformation of the texture from a randomly oriented to well oriented (111) polycrystalline texture, and subsequent reduction in the volume fraction of (100) oriented grains. Interfaces within Co/Cu are found to propagate with a high degree of conformality with increasing bilayer number, with an out-of-plane correlation length well in excess of 300Å. In contrast, the Co/Pt system exhibits a limiting out-of-plane correlation length of the order of 350Å arising from a columnar growth mode. X-ray Reflectivity and Diffraction measurements provide no structural interpretation for the 3-fold enhancement in the rate of increase of the saturation conductivity, as a function of spacer thickness, in Fe/Au (100) compared to Fe/Au (111), or why large oscillations in the GMR occur for the (100) orientation only. Such observations are, however, consistent with the existence of a channelling mechanism in Fe/Au (100). Grazing Incidence Fluorescence data indicates that Nb acts as a surfactant in Fe/Au (111) growth on sapphire. The influence of different defect types within multilayers has also been observed.
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Stevens, Edward Dirk. "X-ray anaomalous scattering studies of D-DNA." Thesis, Keele University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293963.
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Everard, Mark John. "X-ray scattering studies of self-assembled nanostructures." Thesis, University of Leicester, 2004. http://hdl.handle.net/2381/30677.
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The structure and growth of self-assembled nanoparticle networks and epitaxial rare-earth thin-films have been studied using X-ray scattering.;A diffusive growth model was developed to model the specular reflected X-ray signal monitored at the anti-phase position, during the growth of two rare-earth (RE) metals, gadolinium and samarium onto molybdenum(110) single crystals. The model identifies atomic layer spacings and the degree of interlayer mass transport. Both RE elements are shown to grow in a layerwise manner but with significant roughness after the initial layer is occupied. The RE growth mode was modified by raised substrate temperatures. The presence of pre-deposition oxygen at the surface was found to encourage layer-by-layer growth for both Gd and Sm.;The structure of noble-metal nanoparticles passivated with thiolate organic ligands was studied using small and wide angle X-ray scattering (SAXS/WAXS). Ag nanoparticles were found to consist of a spherical metal core with fcc atomic packing. The passivating shell was modified to induce direct cross-linking between nanoparticles. The structure and development of the nanoparticle aggregates formed due to the interactions between functionalised thiol derivatives of porphyrin, benzene, C5 dithiol and MUA was monitored with SAXS. In all cases the structures were found to be open and fractal, with the size of the cross-link determined by the size of the functionalised ligand.;The structural quality of self-assembled noble-metal nanoparticle superlattices was investigated using GISAXS. Au nanoparticle networks were formed at the air/water interface. Fits to the GISAXS data, revealed that strain build-up in the layer can directly control the interparticle spacing. Larger Au nanoparticles were allowed to self-assembly onto a Si(111) substrate. The influence of the substrate temperature prior to assembly was investigated and revealed a striking phase transition below 16.7°C from disordered nanoparticle networks to highly ordered layered nanoparticle structures. It is thought that solvent volatility plays a crucial role in the ordering process.
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Moreno, Carrascosa Andrés. "Theory of elastic and inelastic X-ray scattering." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31442.
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X-rays have been widely exploited to unravel the structure of matter since their discovery in 1895. Nowadays, with the emergence of new X-ray sources with higher intensity and very short pulse duration, notably X-ray Free Electron Lasers, the number of experiments that may be considered in the X-ray regime has increased dramatically, making the characterization of gas phase atoms and molecules in space and time possible. This thesis explores in the theoretical analysis and calculation of X-ray scattering atoms and molecules, far beyond the independent atom model. Amethod to calculate inelastic X-ray scattering from atoms and molecules is presented. The method utilizes electronic wavefunctions calculated using ab-initio electronic structure methods. Wavefunctions expressed in Gaussian type orbitals allow for efficient calculations based on analytical Fourier transforms of the electron density and overlap integrals. The method is validated by extensive calculations of inelastic cross-sections in H, He+, He, Ne, C, Na and N2. The calculated cross-sections are compared to cross-sections from inelastic X-ray scattering experiments, electron energy-loss spectroscopy, and theoretical reference values. We then begin to account for the effect of nuclear motion, in the first instance by predicting elastic X-ray scattering from state-selected molecules. We find strong signatures corresponding to the specific vibrational and rotational state of (polyatomic) molecules. The ultimate goal of this thesis is to study atomic and molecular wavepackets using time-resolved X-ray scattering. We present a theoretical framework based on quantum electrodynamics and explore various elastic and inelastic limits of the scattering expressions. We then explore X-ray scattering from electronic wavepackets, following on from work by other groups, and finally examine the time-resolved X-ray scattering from non-adiabatic electronic-nuclear wavepackets in the H2 molecule, demonstrating the importance of accounting for the inelastic effects.
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Hobbs, Sarah. "Development of resonant inelastic X-ray scattering spectroscopy." Thesis, University of Southampton, 2012. https://eprints.soton.ac.uk/349475/.
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This research focuses on the development of Resonant Inelastic X-ray Scattering spectroscopy (RIXS) as a tool in homogeneous catalysis by looking at 3d transition metal compounds and specifically Cr(salen) epoxidation catalysts. Previous studies have demonstrated the sensitivity of transition metal K-edge X-ray absorption pre-edge and edge features to their chemical environment, but the exact origins are unassigned. The aim of this study is to bring together a collection of complementary, and some novel, X-ray techniques to assign these features and obtain more detailed structural and electronic information on the systems under investigation. Novel high energy resolution data on transition metal complexes have been obtained and the pre-edge region has been simulated with the FEFF9 multiple scattering code. The increase in spectral structure compared to normal XANES allows for a more detailed analysis and as such, provides detailed insights in the electronic properties. L-edge XAS data obtained using soft X-rays enabled the determination of crystal field parameters, which were compared with other X-ray (RIXS) and optical absorption techniques. The novel RIXS experiments provide L and K-edge spectra unaffected by lifetime broadening or background from the main absorption edge. 2D images of X-ray emission as a function of absorption are obtained, revealing the relationship between them and providing direct and detailed information on the presence and position of molecular orbitals. These 1s2p RIXS experiments make use of hard X-rays enabling in-situ experiments, which are important in the field of catalysis, making it a promising tool to monitor the changing electronics of the metal centre as well as ligand coordination during the catalytic process. Whereas the electronic differences on the Cr metal as a function of salen ligand are not revealed by the current RIXS experiments, which is likely due to resolution issues, new preliminary insights in the different catalytic Cr intermediates of the epoxidation reaction have been obtained.
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Soininen, Aleksi. "Final-state interactions in inelastic X-ray scattering." Helsinki : University of Helsinki, 2001. http://ethesis.helsinki.fi/julkaisut/mat/fysii/vk/soininen/.
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Botez, Cristian E. "Synchrotron x-ray scattering studies of metallic surfaces /." free to MU campus, to others for purchase, 2002. http://wwwlib.umi.com/cr/mo/fullcit?p3052151.
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Lawrence, Shane Michael. "X-ray and neutron scattering of multiferroic LuFe2O4." Thesis, Curtin University, 2011. http://hdl.handle.net/20.500.11937/1336.
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Multiferroic materials have recently begun to attract significant scientific interest due to their potential applications in the design of modern electronic devices. Currently, the magnetic properties of materials form the basis of our electronic data storage and have the potential to enhance the logic operations performed in electronic devices (such as computers and sensors). Non-volatile magnetic memory is used in data storage devices, such as the hard drives found in personal computers, where data is encoded via the magnetisation state of magnetic domains in the device with one of two states: either up or down (M ↑ or M ↓); the state is determined or changed by interacting with the magnetic flux about the domain. Furthermore, in current computing and sensor technology, logic operations are performed with arrays of transistors; however, in spintronics ("spin transport electronics") the electric current itself is spin polarised and there is data encoded in the current itself. Circuit elements in such a system are magnetic devices that interact with the electron spin.Magnetoelectric multiferroics are materials that have both a spontaneous ferroelectric polarisation (P) and magnetic magnetisation (M). Polarisation may be manipulated by an electric field and magnetisation by a magnetic field, hence the potential of multiferroics lies in the coupling between the two degrees of freedom and the manipulation of magnetisation by an applied electric field and vice versa. The properties of a magnetic device could be altered "on-the-fly" by applying an electric pulse, and in the context of the examples provided this would greatly diversify the logic elements in spintronic circuits. Furthermore, with both polarisation and magnetisation a multiferroic domain can take on one of four states (M ↑ P ↑, M ↑ P ↓, M ↓ P ↑, or M ↓ P ↓) dramatically increasing data storage density over the current binary system.Lutetium ferrite (LuFe2O4) is a multiferroic material in which both the magnetisation and polarisation arise from the iron sites and with strong iron-iron correlations the material is a promising candidate as a high temperature multiferroic. The material has a layered structure with bilayers of FeO separated by single layers of LuO on a hexagonal lattice. Frustrated 2D charge order exists below 550 K which transitions to 3D charge order below 330 K and simultaneously frustrated ferrimagnetic order exists in the multiferroic phase below 250 K. X-ray and neutron scattering experiments have been performed in order to characterise the ferroelectric and ferrimagnetic order and magnetoelectric coupling in this material.Resonant x-ray scattering (RXS) was performed on the Material Science beamline of the Swiss Light Source where the energy dependence of the superlattice reflections corresponding to the charge order was collected. Non-linear regression using a custom Levenberg-Marquadt algorithm was applied in order to extract the anomalous scattering factors which demonstrated the superlattice reflections were described by a charge order model. Furthermore, the chemical shift was shown to correspond to full Fe2+/Fe3+ charge disproportionation. The absence of any polarisation or azimuthal dependence, shown by resonant x-ray scattering data collected on the ID20 beamline of the European Synchrotron Radiation Facility, confirmed the prediction of Nagano et al. that the orbital moments of the Fe2+-sites exist in a disordered glassy state.X-ray absorption near edge structure (XANES) calculations were performed using the FDMNES program in order to assess the validity of the anomalous scattering factors obtained in the RXS experiment and to further test the charge order model. It was shown that the characteristic features of the experimentally determined functions can be qualitatively reproduced by calculations using the known charge order model. Furthermore, these functions were shown to reproduce the phase of the RXS data further demonstrating that the reflections result from a pure charge ordered phase.Inelastic neutron scattering performed on the PUMA triple axis spectrometer of the FRMII demonstrated that magnetic critical scattering is observed at 250 K. A broad peak in the temperature dependence is observed rather than the characteristic divergence of a magnetic transition: this is attributed to broadening of the transition by the distribution of oxygen stoichiometry in the sample and ferroelectric fluctuations integrated into the data due to poor c-axis resolution. Pyroelectric current and magnetometry measurements demonstrate a peak in the magnetic susceptibility and a step in the polarisation at approximately 215 K, well below the magnetic transition. Elastic neutron scattering experiments performed on the E2 flat cone diffractometer of the Helmholtz-Zentrum Berlin demonstrate these features correspond to a 2D-to-3D magnetic transition that has previously only been predicted by anomalies in other measurements.An applied field study performed by neutron scattering on the E2 flat cone diffractometer of the Helmholtz-Zentrum Berlin and x-ray scattering on the PX1 protein crystallography beamline of the Australian synchrotron demonstrate the control of the magnetic domain population with an electric field, contrary to other recent reports on this topic. Furthermore, the observed magnetoelectric coupling is inconsistent with current models of the magnetic structure of this system. The x-ray measurements demonstrate a disorder-to-order effect by the applied electric field as 3D order is preferred with an increase in the intensity of all satellites.Temperature dependent x-ray powder diffraction data collected on the Powder Diffraction (PD) beamline of the Australian Synchrotron has demonstrated anisotropic thermal expansion with negative thermal expansion of the c-axis in this material. Electron density mapping by Fourier analysis shows the disorder of the oxygen between the electrically static Lu ions and the neighbouring Fe ions, as electron hopping between Fe2+ and Fe3+ leading to a corresponding variation on the Fe-O bond length. Reversible structural distortions are observed indicating a piezoelectric effect in this material caused by the crushing during sample preparation. Furthermore, weak reflections in the x-ray patterns, corresponding to a monoclinic sublattice, suggest a monoclinic distortion of the oxygen sites which is supported by neutron powder diffraction collected on the ECHIDNA instrument of the OPAL reactor.
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Loergen, Marcus. "Coherent soft X-ray magnetic scattering and lensless imaging." [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=971979391.
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Reynolds, David John. "An X-ray scattering study of surfactant-water mixtures." Thesis, University of Central Lancashire, 1988. http://clok.uclan.ac.uk/19984/.
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The occurrence of nematic and lamellr mesophases in concentrated surfactant / water mixtures is a well documented phenomenon. This work examines the structure and order of the mesophases exhibited by two sample systems, caesium pentadecafluorooctanoa-te (CsPFO) / heavy water, and decylammonium chloride / ammonium chloride / heavy water, and their dependence on temperature and composition. The results obtained are discussed with relatIon to inter- and intra-micellar interactions leading to the proposition of an attractive intermicellar interaction at high surfactant concentration.
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Minkov, Ivaylo. "Nuclear Dynamics in X-ray Absorption and Raman Scattering." Doctoral thesis, Stockholm : Theoretical Chemistry, Royal Institute of Technology, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3902.
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Großmann, Günter [Verfasser]. "Solution X-ray scattering studies of metalloproteins / Günter Großmann." Karlsruhe : KIT-Bibliothek, 1993. http://d-nb.info/1138708348/34.
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Bassi, Andrea Li. "X-ray and light scattering from nanostructured thin films." Thesis, Durham University, 2000. http://etheses.dur.ac.uk/4631/.
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The object of this thesis is the study of nanostructured thin films using inelastic fight scattering and elastic x-ray scattering techniques. Their use in combination with other techniques is a powerful tool for the investigation of nanostructured materials. X-ray, Raman and Brillouin characterisation of cluster-assembled carbon films, promising for applications in the field of catalysis, hydrogen storage and field emission, is here presented. X-ray reflectivity (XRR) provided a measure of the density. Raman spectroscopy showed that the local bonding in these amorphous films depends on the size distribution of the clusters and that it is possible to select the cluster size in order to grow films with tailored properties. Brillouin scattering provided a characterisation at the mesoscopic scale and an estimate of the elastic constants, revealing a very soft material. XRR was employed to study density, layering and roughness of a wide range of amorphous carbon films grown with different techniques. Some films possess an internal layering due to plasma instabilities in the deposition apparatus. By comparing XRR with Electron Energy Loss Spectroscopy, a unique value for the electron "effective mass" was deduced and a general relationship between sp(^3)-content and density was found. XRR and H effusion were used to determine the hydrogen content. A study of the size-dependent melting temperature in tin nanoparticle thin films was undertaken with a combined use of X-Ray Diffraction (XRD) and light scattering. A redshift in the position of a Rayleigh peak in the temperature-dependent Brillouin measurements was shown to be related to the melting of the nanoparticles and explained by an effective medium model. XRD also provided information on the low-level of stress in the particles. Low-frequency Raman scattering was used to study the behaviour of the acoustic modes of a single particle as a function of temperature.
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Medway, Stuart Lambert. "In-situ X-ray scattering studies of nickel electrochemistry." Thesis, University of Liverpool, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.408555.
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Fairbrother, P. J. "Thermal diffuse scattering in energy-dispersive x-ray spectroscopy." Thesis, University of Exeter, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.232967.
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Ramos, Silvia. "Resonant X-ray scattering studies of concentrated aqueous solutions." Thesis, University of Bristol, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.393020.
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Dean, Philip Richard. "Resonant soft X-ray scattering from complex magnetic structures." Thesis, Durham University, 2016. http://etheses.dur.ac.uk/12302/.
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This thesis lays out a number of investigations into different magnetic systems governed by short- and long-range magnetic interactions. We take advantage of the sensitivity of soft x-rays to magnetism and the polarisation dependence of magnetic x-ray scattering to investigate these systems. Full polarisation analysis is a highly sensitive technique which can be utilised to refine small deviations in magnetic structures. We present work on improving the efficiency of these measurements, finding efficiencies of up to 75% in the measurement method by rotating the incident light angle with the polarisation analyser fixed at the peak of intensity. Full polarisation analysis has been applied to the study of magnetism in the heavy fermion system CeRu₂Al₁₀. Although this system has a relatively simple magnetic structure it is highly unstable to doping and has an anomalously high transition temperature. Magnetic scattering was observed at the cerium M-edges and the polarisation dependence of the scattering is only consistent with a non-collinear magnetic structure. Least squares fitting of the non-collinear structure revealed a small spin canting of the magnetic structure towards the a-axis. This canting requires a symmetry lowering of the space group from Cmcm to the subgroup Pmnm to allow for the Dzyaloshinskii-Moriya interaction. Full polarisation analysis as well as neutron powder and single crystal measurements have been undertaken on the multiferroic skyrmion system Cu₂OSeO₃. Measurements were taken in the helical, conical, skyrmion, and ferrimagnetic regions. The (1, 0, 0) reflection at the Cu L-edge was found to be due to the anisotropy of the tensor of x-ray susceptibility (ATS). The satellite reflections around the ATS peak were observed not to display the polarisation dependence expected for a helix. The polarisation dependence observed is not consistent with a non-collinear structure and can be fitted with a long spin density wave with the moment pointing along the scattering vector. This structure would be expected to produce stepped features in the magnetisation measurements which are not observed. This long spin density wave structure is also not consistent with previous Lorentz transmission electron microscopy measurements. Neutron scattering measurements confirm the three up one down magnetic structure in the ferrimagnetic phase. However, the magnetic intensity at the (1, 0, 0) position in the helical phase indicates a change in the magnetic structure Rietveld refinement fitting with a reduced ferrimagnetic structure where one of the $4a$ site copper moments is coupled antiferromagnetically to the 12b and remaining 4a site moments. Finally, the magnetic properties of thin films have been investigated using absorption techniques and x-ray magnetic circular dichroism. Manganese oxide monolayers and bilayers have been grown in different charge environments provided by heterostructuring with SrTiO₃ and LaAlO₃, with the aim of controlling the magnetic properties of the manganese via charge transfer. It was found that the magnetic properties of the manganese is strongly linked to the capping layer used. This is due to different effects introduced by the growth of the different capping layers; LaAlO₃ introducing strong ion intermixing, and SrTiO₃ introducing oxygen vacancies. Both capping layers displayed superparamagnetic temperature and field dependent properties with small clusters (around 4) of strongly interacting manganese ions. The strongly interacting manganese ions are separated by either the ion intermixing or oxygen vacancies. Both capping layers displayed superparamagnetic temperature and field dependent properties. Superparamagnetism is usually only observed in nanoparticles. The elimination of the magnetic interactions required for nanoparticle-like properties to be possible are due to a combination of ion intermixing and oxygen vacancies.
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Choi, Sungkyun. "Neutron and X-ray scattering studies of honeycomb iridates." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:d47c4e67-14c6-43ea-a8ba-47b9201b5002.
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This thesis presents neutron and x-ray scattering measurements on quasi-two-dimensional honeycomb antiferromagnets A2IrO3 (A=Na, Li) and the solid-solution intermediate material (Na1-xLix)2IrO3. The aim is to study the magnetic order and excitations of 5d Ir4+ ions in a honeycomb lattice, where unusual magnetic properties have been theoretically predicted to be stabilised by the combinations of strong spin-orbit coupling and honeycomb lattice geometry with 90 degree Ir-O-Ir bonding. By using an optimised setup to minimise the strong neutron absorption by Ir nuclei, inelastic neutron scattering measurements on powder sample of Na2IrO3 observed dispersive excitations below 5meV with a dispersion that can be accounted for by including substantial further-neighbor exchanges that stabilize zigzag magnetic order. The onset of long-range magnetic order was confirmed by the observation of oscillations in zero-field muon-spin rotation experiments. Higher-resolution inelastic neutron data found features consistent with a spin gap of 1.8meV and the data was parameterised by including Ising-type exchange anisotropy. Combining single-crystal diffraction and density functional calculations, a revised crystal structure model with significant departures from the ideal 90 degree Ir-O-Ir bonds required for dominant Kitaev exchange was proposed. Various "idealised'' crystal structures were constructed to emphasize the departures between the actual structure and structures with cubic IrO6 octahedra. The magnetic excitations from the isostructural Li2IrO3 revealed strongly dispersive magnetic excitations, qualitatively different from Na2IrO3. Elastic neutron diffraction detected a magnetic Bragg peak with a wavevector consistent with spiral orders. To explain the observed neutron data, the spiral H2 phase in the Heisenberg J1-J2-J3 model was proposed, and a full calculation was performed with strong in-plane anisotropic interaction. A further measurement for improving the lower-energy excitation found no clear evidence for a spin gap down to E=0.7meV. Lastly, the crystal structure of (Na1-xLix)2IrO3 was investigated with single-crystal x-ray diffraction, revealing a site-mixing of Ir and Na ions in the honeycomb lattice and insensitivity of the refinement to the Li positions. Ab initio calculations suggested that up to x=0.25 Li ions replaced Na in the honeycomb centre and phase separation occurred beyond that, which is consistent with the evolution of observed lattice parameters.
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Johnstone, Graeme Eoin. "Neutron and X-ray scattering study of magnetic manganites." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:a19f8d08-8468-489d-a959-1002af0c9dec.
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This thesis presents three investigations of the magnetic and electronic proper- ties of manganese oxide materials. The investigations are performed using a variety of neutron scattering and x-ray scattering techniques. The electronic ground-state of Pr(Sr0.1 Ca0.9)2 Mn2O7 an antiferromagnet with CE-type ordering, is determined using neutron spectroscopy, as opposed to the more usual approach of using diffraction. The Zener polaron model of the elec- tronic ground state of the CE-type magnetic phase is shown to be unsuitable for this material. The ground-state is shown to agree well with the electronic ground state proposed by Goodenough in the 1950’s, but without significant Mn3+/Mn4+ disproportionation. The distribution of the magnetisation density within the unit cell of the CE-type antiferromagnet La0.5Sr1.5MnO4 is determined from a polarised neutron diffraction experiment by analysing the results with the maximum entropy method. The majority of the magnetisation density is found to be located at the Mn site. The investigation shows tentative evidence of a small magnetic moment on the in-plane O site. However, a larger moment is observed at both the La/Sr site and the out-of-plane O site. The magnetic structure of the magnetoelectric multiferroic DyMn2O5 is inves- tigated using resonant magnetic x-ray scattering. The magnetic structure is shown to be similar to other members of the RMn2O5 series of multiferroics, but with the key difference that the magnetic moments are closely aligned parallel with the crystallographic b-axis, in contrast to the usual observation of the moments being close to parallel with the a-axis. This study also shows evidence that the electrical polarisation has a significant contribution from the valence electrons of the O ions, agreeing with previous work.
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Williams, Richard Paul. "X-ray scattering studies on self-assembled alloy structures." Thesis, University of Leicester, 2007. http://hdl.handle.net/2381/30596.
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X-ray scattering has been used to determine the alloy structure of GdFe2 and the real-time formation of nanoparticle assemblies. Initial growth curve analysis on the individual deposition of Gd and Fe allowed the correct stoichiometric ratio of the two species to be co-evaporated and annealed to form the alloy structure GdFe2- The structure of the [1/3 1/3] reconstruction has been determined. The Patterson map obtained from the structure factors at zero perpendicular momentum transfer shows that the Fe atoms are laterally displaced from their predicted positions. Structure factor data for the out-of-plane atomic positions shows that the Gd atoms sit in adsorption sites that are 22% higher than predicted hard sphere positions. Gold nanoparticles of various sizes coated with organic thiol molecules have been studied by X-ray diffraction. The self-assembly process on to a Si(III) substrate was probed in real-time by GISAXS which showed for the first time that the largest particles drop out of solution first and act as seeds for the smaller particles which infringe on the surface minutes later surrounding the larger particle domains. The intermixing of two particles with average size ratio 0.58 showed evidence for a self-assembled bimodal alloy structure which was indicated by missing intensity from a 2 peak Gaussian fit which could be accommodated for by a central 3rd peak. Self-assembly of thiol stabilised gold nanoparticles has been shown to occur at the solvent-air interface. The quality of self-assembly depends strongly on the size of the particles and the evaporation rate of the solvent. A random walk model was used to explain that as the solvent evaporation rate is significantly slowed the nanoparticles are restricted to vertical diffusion only but at room temperatures the particles can diffuse in all directions a result that is further emphasized by the increased level of ordering at cooler temperatures. A complete self-assembly procedure has been suggested where particles above a certain size (1 nm radius) can immediately self-assemble at the solvent-air interface to be later deposited on to the substrate where the thiol ligands can lock the particles into a tight self-assembled layer.
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Couto, Rafael Carvalho. "Coupled electron-nuclear dynamics in inelastic X-ray scattering." Universidade Federal de Goiás, 2016. http://repositorio.bc.ufg.br/tede/handle/tede/7510.
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Esta tese dedicada a estudos tericos e experimentais de espalhamento ressonante inelstico de raios-X (Resonant inelastic X-ray scattering - RIXS) de molculas de monxido de carbono e gua em fase gasosa. Usando estado da arte clculos ab initio de estrutura eletrnica e formalismo de pacotes de onda dependente do tempo, uma anlise completa dos espectros RIXS experimental dos dois sistemas moleculares foi realizada. Na anlise do CO RIXS, fomos capazes de reproduzir o experimento RIXS com excelente preciso, permitindo uma descrio completa dos espectros experimentais. Interferncia entre diferentes canais RIXS correspondentes disperso via orbitais moleculares ortogonais no estado excitado do CO descrito. Com a ajuda do espectro de alta resoluo e simulaes ab initio, mostramos a quebra da aproximao de Born-Oppenheimer na regio onde estados nais de Rydberg acoplam com o estado nal de valncia. Explicamos a formao de uma caracterstica espectral, que foi atribuda a um nico estado em estudos anteriores. Alm disso, atravs da combinao experimento-teoria, aprimoramos o mnimo do potencial do estado excitado de valncia E 1 , juntamente com o constante de acoplamento entre o estado de valncia e dois estados de Rydberg. A m de estudar a gua, desenvolvemos uma nova abordagem terica para descrever molculas triatmicas atravs do formalismo de propagao de pacote de ondas, que reproduz com grande preciso a estrutura vibracional os espectros experimentais RIXS de alta resoluo, permitindo obter importantes concluses. Ns demonstramos que, devido ao acoplamento dos modos vibracionais e anarmonicidade do potencial no estado fundamental e das superfcies de energia potencial do estados excitados, diferentes estados excitados de camada interna em RIXS podem ser usados como portas para sondar diferentes dinmicas de vibrao e para mapear o potencial do estado fundamental usando modos normais de vibrao molecular. O ajuste dos raios-X acima da ressonncia de absoro permite extrair informaes adicionais sobre o potencial do estado fundamental, devido alta excitao vibracional. Substituio isotpica investigada por meio de simulaes tericas e as importantes caractersticas da dinmica nuclear so discutidas, especialmente para o estado excitado de camada interna dissociativo, onde um chamado pico \atmico " formado. Este recurso crucial para explicar a dinmica nuclear em RIXS da gua. Mostramos o forte potencial de experimentos RIXS de alta resoluo combinados IV com simulaes tericas de alto nvel para estudos avanados de estados moleculares altamente excitados, bem como superfcies de energia potencial do estado fundamental, send utilizada como uma tcnica auxiliar para espectroscopia ptica e infra vermelho.
This Thesis is devoted to theoretical and experimental studies of resonant inelastic X-ray scattering (RIXS) of gas-phase carbon monoxide and water molecules. Using state-of-the-art ab initio electronic structure calculations and a time-dependent wave packet formalism, we make a complete analysis of the experimental RIXS spectra of the two molecular systems. In the CO RIXS analysis, we are able to reproduce the RIXS experiment with an excellent accuracy, allowing for a complete description of all experimental features. Interference between di erent RIXS channels corresponding to the scattering via orthogonal molecular orbitals in the core-excited state of CO is described. With the help of the high-resolution spectrum and extensive ab initio simulations we show the complete breakdown of the Born- Oppenheimer approximation in the region where forbidden nal Rydberg states are mixed with a valence allowed nal state. Here we explain the formation of a spectral feature which was attributed to a single state in previous studies. Moreover, through an experimentaltheoretical combination, we improve the minimum of the valence E 1 excited state, along with the coupling constant between the valence and two Rydberg states. In order to study the water system, we developed a new theoretical approach to describe triatomic molecules through the wave packet propagation formalism, which reproduces with high accuracy the vibrational structure of the high-resolution experimental quasi-elastic RIXS spectra, allowing to draw several important conclusions. We demonstrate that due to the vibrational mode coupling and anharmonicity of the ground and core-excited potential energy surfaces, di erent core-excited states in RIXS can be used as gates to probe di erent vibrational dynamics and to map the ground state potential using molecular vibrational normal modes. Tuning the X-rays above the absorption resonance allows to extract additional information about the ground state potential, due to high vibrational excitation. Isotopic substitution is investigated by theoretical simulations and important dynamical features are discussed, especially for the dissociative core-excited state, where a so-called \atomic" peak is formed. This feature is crucial to explain the nuclear dynamics in RIXS from water. We show the strong potential of high-resolution RIXS experiments combined with high-level theoretical simulations for advanced studies of highly excited molecular states, as well as of ground state potential energy surfaces, as an auxiliary technique to optical and IR spectroscopy.
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Velkov, Yasen. "Quantum nuclear dynamics in x-ray scattering and lasing." Doctoral thesis, Stockholm : Bioteknologi, Kungliga Tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9728.
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Elliott, William C. "Low temperature Ag homoepitaxy : an x-ray scattering study /." free to MU campus, to others for purchase, 2000. http://wwwlib.umi.com/cr/mo/fullcit?p9988658.
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Feng, Yejun. "Exciton spectroscopy using non-resonant x-ray Raman scattering /." Thesis, Connect to this title online; UW restricted, 2003. http://hdl.handle.net/1773/9642.
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Rahn, Marein. "Magnetism in quantum materials probed by X-ray and neutron scattering." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:a20ff25c-bc04-44a2-8a29-d5236a06bd83.
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In his programmatic article More Is Different (1972), Nobel laureate P. W. Anderson captured the fundamental interest in quantum matter in a nutshell. The central motive in this field is emergence. In the inaugural volume of the homonymous journal, J. Goldstein defined this as "the arising of novel and coherent structures, patterns and properties during the process of self-organization in complex systems". Famously, the idea that the "the whole is greater than the sum of its parts" goes back to Aristotle's metaphysics, and it has served as a stimulating concept in 19th century biology, economics and philosophy. The study of emergence in condensed matter physics is unique in that the underlying complex systems are sufficiently "simple" to be modelled from first principles. Notably, the emergent phenomena discovered in this field, such as high-temperature superconductivity, giant magnetoresistance, and strong permanent magnetism have had an enormous impact on technology, and thus, society. Historically, there has been a distinction between materials with localized, strongly interacting (or correlated) electrons - and non-interacting, itinerant electronic states. In the last decade, several new states of matter have been discovered, which emerge not from correlations, but from peculiar symmetries (or topology) of itinerant electronic states. The term quantum materials has therefore become popular to subsume these two strands of condensed matter physics: Electronic correlations and topology. In this thesis, I report investigations of four quantum materials which each illustrate present key interests in the field: The mechanism of high temperature superconductivity, the search for materials that combine both electronic correlations and non-trivial topology and novel emergent phenomena that arise from the synergy of electronic correlations and a strong coupling of spin- and orbital degrees of freedom. The common factor and potential key to understanding these materials is magnetism. My experimental work is focused on neutron and x-ray scattering techniques, which are able to determine both order and dynamics of magnetic states at the atomic scale. I illustrate the full scope of these methods with experimental studies at neutron and synchrotron radiation facilities. This includes both diffraction and spectroscopy, of either single- or polycrystalline samples. My in-depth analysis of each dataset is aided by structural, magnetic and charge transport experiments. Thus, I provide a quantitative characterization of magnetic fluctuations in an iron-based superconductor and in two Dirac materials, and determine the magnetic order in a Dirac semimetal candidate and a complex oxide. As a whole, these results demonstrate the elegant complementarity of modern scattering techniques. Although such methods have a venerable history, they are presently developing at a rapid pace. Several results of this thesis have only been enabled by very recent instrumental advances.
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Sellberg, Jonas A. "X-ray scattering and spectroscopy of supercooled water and ice." Doctoral thesis, Stockholms universitet, Fysikum, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-103009.
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This thesis presents experimental studies of water and ice at near-atmospheric pressures using intense x-rays only accessible at synchrotrons and free-electron lasers. In particular, it focuses on the deeply supercooled, metastable state and its implications on ice nucleation. The local structure of the liquid phase was studied by x-ray scattering over a wide temperature range extending from 339 K down to 227 K. In order to be able to study the deeply supercooled liquid, micron-sized water droplets were evaporatively cooled in vacuum and probed by ultrashort x-ray pulses. This is to date the lowest temperature at which measurements of the structure have been performed on bulk liquid water cooled from room temperature. Upon deep supercooling, the structure evolved toward that of a low-density liquid with local tetrahedral coordination. At ~230 K, where the low-density liquid structure started to dominate, the number of droplets containing ice nuclei increased rapidly. The estimated nucleation rate suggests that there is a “fragile-to-strong” transition in the dynamics of the liquid below 230 K, and its implications on water structure are discussed. Similarly, the electronic structure of deeply supercooled water was studied by x-ray emission spectroscopy down to 222 K, but the spectral changes expected from the structural transformation remained absent and explanations are discussed. At high fluence, the non-linear dependence of the x-ray emission yield indicated that there were high valence hole densities created during the x-ray pulse length due to Auger cascades, resulting in reabsorption of the x-ray emission. Finally, the hydrogen-bonded network in water was studied by x-ray absorption spectroscopy and compared to various ices. It was found that the pre-edge absorption cross-section, which is associated with distorted hydrogen bonds, could be minimized for crystalline ice grown on a hydrophobic BaF2(111) surface with low concentration of nucleation centers.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript. Paper 5: Manuscript. Paper 6: Manuscript.
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Hart, John Francis. "A new multiple scattering technique for X-ray photoelectron diffraction." Thesis, University of Leicester, 1997. http://hdl.handle.net/2381/30673.
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This thesis is concerned with the development and application of a new method of performing multiple scattering calculations of X-ray Photoelectron Diffraction (XPD) from periodic surfaces. The technique is based on the dynamical theory of Reflection High Energy Electron Diffraction (RHEED), allowing more efficient access to high photoelectron energies (1000eV and above) than is available using present calculational schemes. Convergence tests have been performed to identify the limitations of the present method. The method is applied to two overlayer systems for which XPD experimental data is available, c(2 x 2)S and c(2 x 2)O on Ni(001). For the c(2 x 2)S system, which is relatively well understood and therefore a good test system, data at four emission (take-off) angles is fitted, giving optimum agreement with the S atoms occupying hollow sites at a vertical adsorption height of between 1.30A and 1.35A. The agreement is improved slightly for the lowest two take-off angles by an outward relaxation in the top Ni-Ni layer spacing. Comparison is made with single scattering calculations for the system and the present method shown to be far superior at the lowest take-off angle. This clearly demonstrates the importance of multiple scattering at grazing emission angles. For the c(2 x 2)O system, data at two take-off angles is fitted giving optimum agreement with the O atoms in hollow sites at an adsorption height of 0.75A. By allowing a small outward relaxation in the top Ni-Ni layer spacing, an almost equally good fit to the data is found at an adsorption height of 0.80A. An offcentre bonding site which has been proposed, in which the O atoms are displaced from their hollow sites by 0.3A in the [110] direction has been considered and ruled out.