LD2668 .T4 1947 A3 / Master of Science

published_or_final_version / abstract / Physics / Master / Master of Philosophy

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.

<p>The odd &ndash / odd Tl nuclei with A &ge / 190 have moderate oblate nuclear deformation and show rotational bands built on different quasiparticle excitations. Several phenomena, not yet fully understood, were observed in these nuclei, such as large signature splitting in the yrast band (built on a &pi / h9/2&otimes / &nu / i13/2 configuration), possible non &ndash / axiality of the nuclear shape, etc. In this work the high &ndash / spin states in 194Tl were studied. The 194Tl nuclei were produced in the 181Ta (18O, 5n) 194Tl reaction at a beam energy of 93 MeV and the &gamma / - rays were detected using the AFRODITE array. The obtained extended level scheme of 194Tl is presented and discussed in this work. CSM (Cranking shell model) and TRS (Total Routhians Surface) models were both applied to interpret the results for band 1. The results were compared with the neighboring isotone 193Hg.</p>

The 23Mg(pγ)24Al and 26Al(pγ)27Si astrophysical reactions are expected to be of considerable importance in the nucleosynthesis of A≥20 nuclei in classical novae. Previous studies have indicated that both reactions are dominated by resonant capture to excited states, above the proton-emission thresholds, in the proton-rich nuclei 24Al and 27Si, respectively. Consequently, by determining the nuclear properties of such resonant states it is possible to estimate the 23Mg(pγ)24Al and 26Al(pγ)27Si stellar reaction rates. In this thesis work, excited states in 24Al and 27Si were populated via the 10B(16O, 2n) and 12C(16O, n) heavy-ion fusion-evaporation reactions, respectively. The beams of 16O ions were produced by the Argonne Tandem Linear Accelerator System and prompt electromagnetic radiation was detected using the GAMMASPHERE detector array, which, in the case of the 24Al experiment, was used in coincidence with recoil selection provided by the Argonne Fragment Mass Analyzer. The two γray spectroscopy studies performed in this work allowed level structure determinations below the respective proton-emission thresholds of 24Al and 27Si nuclei, with improved precision on previous work. In addition to this, these studies also allowed a determination of the nuclear properties of proton-unbound astrophysically important γ decaying states, which, in turn, were used to re-evaluate the 23Mg(pγ)24Al and 26Al(pγ)27Si stellar reaction rates. The improved precision of the level energies and unambiguous assignments of resonant states has reduced the relative uncertainties in both the 23Mg(pγ)24Al and 26Al(pγ)27Si stellar reaction rates, constraining the production of A≥20 nuclei in classical novae.

The goal of this work reported here is to test the limits of the ECPSSR theory in the transition region of the low Z1/Z2.

Soft x-ray spectroscopy can provide a wealth of information on the electronic structure of solids. In this work, a suite of soft x-ray spectroscopies is applied to organic and inorganic materials with potential applications in electronic and energy generation devices. Using the techniques of x-ray absorption (XAS), x-ray emission spectroscopy (XES), and x-ray photoemission spectroscopy (XPS), the fundamental properties of these different materials are explored. Cycloparaphenylenes (CPPs) are a recently synthesized family of cyclic hydrocarbons with very interesting properties and many potential applications. Unusual UV/Visible fluorescence trends have spurred a number of theoretical investigations into the electronic properties of the CPP family, but thus far no comprehensive electronic structure measurements have been conducted. XPS, XAS, and XES data for two varieties, [8]- and [10]-CPP, are presented here, and compared with the results of relevant DFT calculations. Turning towards more application-centered investigations, similar measurements are applied to two materials commonly used in solid oxide fuel cell (SOFC) cathodes: La_(1−x)Sr_(x)MnO_(3) (LSMO) and La_(1−x)Sr_(x)Co_(1−y)Fe_(y)O_(3) (LSCF). Both materials are structurally perovskites, but they exhibit strikingly different electronic properties. SOFC systems very efficiently produce electricity by catalyzing reactions between oxygen and petroleum-based hydrocarbons at high temperatures (> 800 C). Such systems are already utilized to great effect in many industries, but more widespread adoption could be had if the cells could operate at lower temperatures. Understanding the electronic structure and operational evolution of the cathode materials is essential for the development of better low-temperature fuel cells. LSCF is a mixed ion-electron conductor which holds promise for low-temperature SOFC applications. XPS spectra of LSCF thin films are collected as the films are heated and gas-dosed in a controlled environment. The surface evolution of these films is discussed, and the effects of different gas environments on oxygen vacancy concentration are elucidated. LSMO is commonly used in commercial fuel cell devices. Here the resonant soft x-ray emission (RIXS) spectrum of LSMO is examined, and it is shown that the inelastic x-ray emission structure of LSMO arises from local atomic multiplet effects.

by Ka-wai Wong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1995. / Includes bibliographical references (leaves 106-109). / TABLE OF CONTENTS --- p.i / ABSTRACT --- p.v / LIST OF FIGURES --- p.vi / LIST OF TABLES --- p.xi / LIST OF ABBREVIATIONS --- p.x / Chapter Chapter 1 --- Research Background --- p.1 / Chapter 1.1 --- Introduction --- p.1 / Chapter 1.2 --- The effect of solid acceptance angle --- p.2 / Chapter 1.3 --- Research goals --- p.4 / Chapter 1.3.1 --- Determination of the electron spectrometer transmission function --- p.4 / Chapter 1.3.2 --- Novel depth profiling technique by adjusting the solid acceptance angle --- p.6 / Chapter 1.3.3 --- Correction to conventional ARXPS --- p.8 / Chapter 1.4 --- Thesis Structure --- p.8 / Chapter Chapter 2 --- Fundamentals of X-ray Photoelectron Spectroscopy --- p.9 / Chapter 2.1 --- Introduction --- p.9 / Chapter 2.2 --- X-ray Photoelectron Spectroscopy (XPS) --- p.9 / Chapter 2.2.1 --- Basic principles --- p.9 / Chapter 2.2.2 --- Surface sensitivity --- p.11 / Chapter 2.2.3 --- A typical XPS spectrum --- p.13 / Chapter 2.3 --- Qualitative analysis --- p.16 / Chapter 2.3.1 --- Binding energy --- p.16 / Chapter 2.3.2 --- Chemical state information --- p.17 / Chapter 2.4 --- Quantitative analysis --- p.20 / Chapter 2.4.1 --- Factors affecting intensity --- p.20 / Chapter 2.4.2 --- Homogeneous materials --- p.22 / Chapter 2.4.3 --- Layer structure --- p.23 / Chapter Chapter 3 --- Instrumentation --- p.26 / Chapter 3.1 --- XPS spectrometer --- p.26 / Chapter 3.1.1 --- Magnetic immersion lens system --- p.26 / Chapter 3.1.2 --- Tunable iris --- p.29 / Chapter 3.1.3 --- Scan plates --- p.29 / Chapter 3.1.4 --- Input lens aperture --- p.32 / Chapter 3.2 --- Calibration of the iris --- p.32 / Chapter 3.3 --- Applications --- p.35 / Chapter 3.3.1 --- Two dimensional XPS imaging --- p.35 / Chapter 3.3.2 --- ARXPS --- p.37 / Chapter 3.4 --- Summary --- p.37 / Chapter Chapter 4 --- Determination of electron spectrometer transmission function --- p.38 / Chapter 4.1 --- Introduction --- p.38 / Chapter 4.2 --- Traditional method of determination --- p.39 / Chapter 4.3 --- Methodology of the novel approach --- p.40 / Chapter 4.4 --- Calculation Procedures and Results --- p.48 / Chapter 4.5 --- Results and Discussions --- p.50 / Chapter 4.6 --- Conclusions --- p.57 / Chapter Chapter 5 --- "Depth Profiling by Adjusting the Solid Acceptance Angle: a Starting Point to “ Three-Dimensional Imaging""" --- p.59 / Chapter 5.1 --- Introduction --- p.59 / Chapter 5.2 --- Theoretical Background --- p.60 / Chapter 5.2.1 --- Quantification of Intensity --- p.60 / Chapter 5.3 --- Experimental --- p.69 / Chapter 5.3.1 --- Operation --- p.69 / Chapter 5.3.2 --- Calibration of iris --- p.70 / Chapter 5.3.3 --- Novel depth profile by adjusting the solid acceptance angle --- p.71 / Chapter 5.4 --- Results and Discussions --- p.71 / Chapter 5.4.1 --- Depth Profiles --- p.71 / Chapter 5.4.2 --- "Concept of ""Three-Dimensional XPS Imaging""" --- p.72 / Chapter 5.5 --- Conclusions --- p.76 / Chapter Chapter 6 --- Correction to Quantitative X-ray Photoelectron Spectroscopy with Consideration of the Solid Acceptance Angle --- p.79 / Chapter 6.1 --- Introduction --- p.79 / Chapter 6.2 --- The effect of the solid acceptance angle --- p.80 / Chapter 6.3 --- Theoretical Background --- p.83 / Chapter 6.4 --- Results and Discussions --- p.87 / Chapter 6.4.1 --- Homogeneous Sample --- p.87 / Chapter 6.4.2 --- Layer structure --- p.90 / Chapter 6.4.3 --- Simulation plots and further investigation --- p.92 / Chapter 6.5 --- Conclusions --- p.101 / Chapter Chapter 7 --- Conclusion --- p.103 / Acknowledgment --- p.105 / References --- p.106

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In the ejecta from ONe novae outbursts nuclei up to A~40 are observed. The 30P(p,γ)31S reaction is thought to be the bottleneck for the production of all elements heavier than sulphur. However, due to uncertainties in the properties of key proton-unbound resonances the reaction rate is not well determined. In this thesis work, excited states in 31S were populated via the 28Si(4He,n) light-ion fusion-evaporation reaction and the prompt electromagnetic radiation was then detected with the GAMMASPHERE detector array. This γ-ray spectroscopy study, and comparisons with the stable mirror nucleus 31P, allowed the determination of the 31S level structure below the proton-emission threshold and also of the key proton-unbound states for the 30P(p,γ)31S reaction. In particular, transitions from key, low-spin states were observed for the first time. This new information was then used for the re-evaluation of the 30P(p,γ)31S reaction in the temperature range relevant for ONe novae. The newly calculated rate is higher than previous estimates implying a greater flux of material processed to high-Z elements in novae. Astrophysical X-ray bursts are thought to be a result of thermonuclear explosions on the atmosphere of an accreting neutron star. Between these bursts, energy is thought to be generated by the hot CNO cycles. The 15O(α,γ)19Ne reaction is one reaction that allows breakout from these CNO cycle and into the rp-process to fuel outbursts. The reaction is expected to be dominated by a single 3/2+ resonance at 4.033 MeV in 19Ne, however, limited information is available on this key state. This thesis work reports on a pioneering study of the 20Ne(p,d)19Ne reaction in inverse kinematics performed at the Experimental Storage Ring (ESR) as a means of accessing the 4.033-MeV state in 19Ne. The unique background free, high luminosity conditions of the ESR were utilised for this, the first transfer reaction performed at the ESR. The results of this pioneering test experiment are presented along with suggestions for future measurements at storage ring facilities.