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Computational and instrumental developments in quantitative Auger electron analysisJackson, Andrew Robert January 1999 (has links)
No description available.
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Positron moderation and apparatus for low energy electron and positron spectroscopyWilkie, Peter January 2009 (has links)
Surface-analysis and treatment apparatus have been variously designed, manufactured, developed, and commissioned or re-commissioned, for characterising the surfaces and efficiency of positron moderators based around 3 µm thick polycrystalline-tungsten foil. These include XPS and AES, based around a CLAM2 hemispherical analyser, electron-beam heating, ion bombardment, mass spectroscopy, UHV sample mounting, UHV manipulation, gas-handling lines, and entry-lock apparatus. The CLAM2 electron spectrometer is additionally adapted for operation as a bipolar charged-particle spectrometer. All control software, and much data-analysis software, is implemented in Labview. Apparatus and techniques for safely storing, handling, transferring into vacuum, and manipulating in vacuo, a nominally 1 mCi 22Na, UHV-compatible positron source, are designed, constructed, and implemented. The efficacy of cleaning and surface-analysis apparatus are demonstrated, with some limitations and instrument malfunction identified, and solutions implemented. Methods for passivating positron-trapping states in polycrystalline tungsten are proposed, based on the current understanding of positron moderation and trapping. Improved moderator geometries have been designed and an alternative, simpler, and easier to implement solid-gas moderator proposed.
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Pushing the boundaries of condensed matter electron momentum spectroscopyBowles, Cameron Michael Albert, cameronbowles@hotmail.com January 2008 (has links)
An electron momentum spectrometer at the Australian National University has been used to study various aspects of different solid state systems. EMS is a transmission mode technique and involves the collision of the incident electron with a bound electron, after which both electrons are ejected and measured in coincidence. Through well defined reaction kinematics the complete valence
spectral momentum density A(ɛ,q) can be measured. The spectrometer has been used to measure the spectral momentum
densities (spectral functions) of single crystal targets, as well as targets in disordered states. A new spin polarised electron source was constructed and implemented in the ANU spectrometer, which was used to measure spin dependent features of ferromagnetic samples.¶
This thesis is divided into seven chapters, the first chapter is an introduction into the field of electron momentum spectroscopy, highlighting what has been measured before and how the technique has progressed to its present state. Some comparisons to other experimental techniques will be made.¶
The second chapter describes the ANU EMS spectrometer in detail. The technique requires some technical and advanced equipment that is often used in novel ways. The production of thin (20 nm) free standing targets will be detailed, along with the experimental chamber and electronics used to run the apparatus and collect data. The determination of the energy and momentum resolution of the experiment is also described.¶
The third chapter will detail the design and construction of the new spin polarised electron source. The results of commissioning and characterizing the new source will be presented.¶
Chapters four through six will present the measured results. The fourth chapter will detail the single crystalline measurements for the group eleven noble metals (Cu, Ag and Au). Each sample was measured along three high symmetry directions and compared to a DFT calculation using the LDA and a FP-LMTO basis. The fifth chapter will include the results from samples that were in disordered states, a measurement which is unique to the EMS technique. The polycrystalline and amorphous states of the Si and Ge semiconductors are presented and conclusions are made to the degree of difference in the results and to which theoretical approach to the unique amorphous state of the semiconductors best matches the EMS results. The sixth chapter includes results of ferromagnetic iron, measured using the spin polarised electron source. The spectrometer was used to measure spin-polarised electron-energy-loss-spectroscopy (SPEELS) and magnetic electron-Compton profiles. A theoretical investigation is also presented in chapter six which details the advancements required in the spin polarised electron gun to measure an accurate spin-polarised EMS spectra of a ferromagnetic Fe sample.¶
Chapter 7 includes the summary of all the results presented and conclusions reached from the comparison of the measured EMS spectra and various theoretical calculations. A discussion is presented about the future directions and possibilities of the EMS technique.
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Study of the decay ¹⁸⁴Au-¹⁸⁴Pt by means of gamma and electron spectroscopy and low temperature nuclear orientationXu, Yue-shu 08 May 1992 (has links)
Graduation date: 1992
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Magnetische und elektronische Eigenschaften von Übergangsmetalloxid-NanostrukturenHellmann, Ingo 29 September 2009 (has links) (PDF)
Die eingereichte Dissertation befasst sich mit Übergangsmetalloxid-Nanostrukturen, wobei quasi-eindimensionale Materialien im Mittelpunkt stehen, z.B. Nanoröhren und Nanostäbe. Mittels Suszeptibilitäts- bzw. EELS-Messungen wurden magnetische und elektronische Eigenschaften verschiedener Nanoverbindungen untersucht. Zur weiteren Charakterisierung der Proben wurden außerdem Magnetisierungsmessungen (VSM, Pulsfeld), optische Spektroskopie, AC-Suszeptibilitätsmessungen, Messungen der spezifischen Wärme sowie NMR- und ESR-Experimente durchgeführt. Ein Schwerpunkt dieser Arbeit sind Vanadiumoxid-Verbindungen, wobei Vanadiumoxid-Nanoröhren (VOxNT) aufgrund ihrer besonderen Morphologie eine Sonderstellung unter den vorgestellten Materialien
besitzen. Suszeptibilitätsmessungen an den VOxNT offenbaren aktiviertes Verhalten bei Temperaturen T > 100 K, was auf V4+-Spindimere zurückgeführt werden kann. Zudem existieren quasi-freie V4+-Momente sowie längere Spinkettenfragmente, z.B. Trimere. Elektronische Anregungen im Valenzband können wahrscheinlich dem Platzwechsel von 3d-Elektronen zwischen V4+- und V5+-Plätzen innerhalb der gemischtvalenten V-O-Ebenen zugeschrieben werden. Durch Dotierung mit Alkalimetallen ist es möglich, die V 3d-Niveaus mit zusätzlichen Elektronen zu besetzen und dadurch die Vanadiumvalenz zu beeinflussen (V5+ -> V4+ -> V3+). Die dabei auftretenden stärkeren Coulombabstoßungen zwischen den V 3d-Elektronen beeinträchtigen die Mobilität der Ladungsträger. Ebenso wurde gezeigt, dass sich durch die Dotierung mit Ammoniak und
anderen Übergangsmetallionen die Vanadiumvalenz sowie der Magnetismus der VOxNT beeinflussen lassen. Die Ergebnisse von weiteren Vanadiumoxid-Nanostrukturen - Co0.33V2O5,
alpha-NaV2O5, VO2(B) sowie V3O7·H2O-Nanokristallen - zeigen, dass sehr unterschiedliches magnetisches Verhalten wie Paarbildung zwischen V4+-Spins, antiferromagnetisch gekoppelte Spinketten oder ein Phasenübergang zwischen zwei paramagnetischen Temperaturbereichen auf Nanoebene realisiert werden kann. Die
magnetischen Eigenschaften von MnO2-Nanostäben sind durch starke Kopplungen und Frustration zwischen den Mn-Spins gekennzeichnet. Außerdem zeigt die Verbindung Merkmale eines Spinglases. Durch Dotierung mit Elektronen lässt sich bei diesem Material die Mn-Valenz verändern. Schließlich zeigen erste Charakterisierungsmessungen
an übergangsmetalldotierten MoO3-Nanobändern paramagnetisches Verhalten dieser Systeme.
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Electronic spectra and structures of metal-oxo complexes /Da Re, Ryan Edward. January 2002 (has links)
Thesis (Ph. D.)--University of Chicago, Department of Chemistry, 2002. / Includes bibliographical references. Also available on the Internet.
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Deposition and spectroscopy of supported metal clustersGrimaud, Christele-Marine January 2000 (has links)
This dissertation describes experimental investigations of deposited atomic clusters and of films of metal particles produced by cluster deposition on graphite. It consists of three chapters presenting a review of the addressed subjects, the experimental techniques, and a summary of the results. The main body of results is described in full in afourth chapter as research papers. A systematic study of the impact of metal cluster trimers on highly oriented pyrolitic graphite (HOPG) is investigated. The creation of defects at the surface of graphite is found to be independento f the masso f the atoms in the two typeso f clusters considered The electron energy loss spectroscopy (EELS) of collective electronic excitations (plasmons) in a film of silver particles is presented A weak positive dispersion of the plasmon mode is measured and exhibits a higher ftequency of the mode with parallel momentum close to zero than in Ag surfaces. The adsorption of cinnamaldehydeis examined on nanostructured palladium surfaces. The EELS spectrum of cinnamaldehyde adsorbed on palladium is presented, as well as that of condensed layers of cinnamaldehyde on HOPG. Findings of this thesis involve different physical and chemical properties of the cluster surface system with a view in using cluster deposition for practical applications such as the investigation of model catalysts.
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Integrating Experiment and Theory in Electrochemical Surface Science: Studies on the Molecular Adsorption on Noble-Metal Electrode Surfaces by Density Functional Theory, Electron Spectroscopy, and ElectrochemistryJavier, Alnald Caintic 16 December 2013 (has links)
Computational techniques based on density functional theory (DFT) and experimental methods based on electrochemistry (EC), electrochemical scanning tunneling microscopy (EC-STM), and high-resolution electron energy loss spectroscopy (HREELS) were employed to study the adsorption of (i) sulfuric acid on Pd(111), (ii) benzene on Pd(111), (iii) hydroquinone/benzoquinone on Pd(111), (iv) hydroquinone sulfonate/benzoquinone sulfonate on Pd(111), (v) 2,3-dimethylhydroquinone/2,3-dimethylbenzoquinone on Pd(111) and polycrystalline Pd, (vi) hydrogen on 1-6 monolayers (ML) of Pd deposited on a Pt(111) substrate, and (vii) a thiolated iron hydrogenase model complex on polycrystalline Au.
In situ EC-STM and DFT investigations of sulfuric acid on a Pd(111) surface indicated that two layers of water molecules and hydronium ions are assembled, non-co-planar with one another, between the rows of surface-coordinated sulfate anions; the layer that is slightly elevated is composed of hydronium counter cations.
The STM images of benzene chemisorbed on a Pd(111) electrode surface were simulated and the results suggested that, when the potential of the Pd electrode is held at 0.3 V, benzene is chemisorbed on a 3-fold site; while at 0.55 V, the molecule is adsorbed on a position between a 3-fold and a 2-fold site.
Computational and experimental results implied that at low concentrations, hydroquinone sulfonate undergoes oxidative chemisorption forming benzoquinone sulfonate (BQS) on the Pd(111) surface, BQS adopts a flat orientation in which the quinone ring is centered over a 2-fold site, and the C–H and C–S bonds are no longer co-planar with the quinone ring and are slightly tilted, directed away from the surface.
At very dilute concentrations, when hydroquinone (H_(2)Q) undergoes oxidative chemisorption producing benzoquinone oriented flat, albeit with a slight tilt, on the Pd(111) surface, the flat-adsorbed quinone ring is centered on a bridge site where the C_(2) axis is rotated 30degree from the [110] direction of the metal substrate, the p-oxygen atoms are located above two-fold sites, and the ring is slightly puckered with the C–H bonds tilted away from the surface at approximately 20degree.
When 2,3-dimethylH_(2)Q is chemisorbed on the Pd surface, at low concentrations, 2,3-dimethylH_(2)Q is oxidatively chemisorbed producing 2,3-dimethyl-1,4-benzoquinone oriented flat on the surface, the flat-adsorbed rings are centered above 2-fold sites wherein the C=O bonds are pointing 30degree from the [110] direction of the substrate, the para-oxygen atoms are located above bridge sites, the peripheral bonds are tilted away from the surface at ca. 20degree, and at higher concentrations, oxidative chemisorption occurs through activation of the ring’s C–H bonds yielding edge-oriented 2,3-dimethylH_(2)Q.
Electrochemistry and DFT results also implied that at 1-2 ML of Pd on Pt(111), hydrogen is only adsorbed on a hollow site while at 3 ML of Pd or more, atomic hydrogen may be chemisorbed on the 3-fold site or absorbed in the octahedral hole underneath the hollow site.
Using Au electrodes, an unbound iron hydrogenase analogue complex studied was found to slightly catalyze the H_(2) evolution process. However, when the complex was immobilized unto the Au surface, the electrocatalytic activity was greatly improved.
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Imaging Atoms and Molecules with Strong Laser FieldsSmeenk, Christopher 15 April 2013 (has links)
We study multi-photon ionization of rare gas atoms and small molecules by infrared femtosecond laser pulses. We demonstrate that ionization is accurately described by a tunnelling model when many infrared photons are absorbed. By measuring photo-electron and photo-ion spectra, we show how the sub-Ångstrom spatial resolution of tunnelling gives information about electron densities in the valence shell of atoms and molecules. The photo-electron and photo-ion momentum distributions are recorded with a velocity map imaging (VMI) spectrometer. We describe a tomographic method for imaging a 3-D momentum distribution of arbitrary symmetry using a 2-D VMI detector. We apply the method to measure the 3-D photo-electron distribution in elliptically polarized light. Using circularly polarized light, we show how the photo-electron momentum distribution can be used to measure the focused laser intensity with high precision. We demonstrate that the gradient of intensities present in a focused femtosecond pulse can be replaced by a single average intensity for a highly nonlinear process like multi-photon ionization. By studying photo-electron angular distributions over a range of laser parameters, we determine experimentally how the photon linear momentum is shared between the photo-electron, photo-ion and light field. We find the photo-electron carries only a portion of the total linear momentum absorbed. In addition we consider how angular momentum is shared in multi-photon ionization, and find the photo-electron receives all of the angular momentum absorbed. Our results demonstrate how optical and material properties influence the photo-electron spectrum in multi-photon ionization. These will have implications for molecular imaging using femtosecond laser pulses, and controlling the initial conditions of laser generated plasmas.
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ESCA studies of a brass surface subjected to gas-jet enhanced sputteringGovier, R. D. 10 December 1992 (has links)
The inert gas ion bombardment of solid surfaces has
found many uses in the field of analytical chemistry. In
one method of spectrochemical analysis, inert gas ion
bombardment in a glow discharge is used to produce an atomic
vapor, representative of the sample bulk, which is analyzed
using atomic absorption techniques. Gas jets directed at
the sample surface during the discharge increase the removal
rate of sample material from the surface. Such bombardment
of solid surfaces results in changes to the surface which
are visually evident in the formation of craters and surface
deposits. This thesis was designed to gain a better
understanding of the changes in a brass surface caused by
jet-enhanced sputtering. Electron spectroscopy for chemical
analysis (ESCA) is used to study selected regions of the
surface. Changes in chemical composition were observed as
successive atomic layers were removed from the sample.
The results of this investigation indicate that the
effects of ion bombardment can be explained in terms of the
selective sputtering of one bulk component over another.
The surfaces of the sputtered craters were found to be
depleted of the higher sputtering yield component, Zn, when
compared to the bulk composition. In a deposit, the
component with the highest sputtering yield was found to be
more concentrated in layers closest to the bulk material.
The component with the lowest sputtering yield was found at
relatively higher concentrations nearest the deposit
surface. The component with the higher sputtering yield is
selectively sputtered first during the glow discharge, and
consequently is deposited with a higher concentration
closest to the bulk, the converse being true for the lowest
sputtering yield component. / Graduation date: 1993
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