Call number: LD2668 .T4 1943 W3 / Master of Science

Digitized by Kansas Correctional Industries

Tam Yi Mei. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references. / Abstracts in English and Chinese. / Abstract --- p.ii / 摘要 --- p.iii / Acknowledgement --- p.iv / Table of Contents --- p.v / List of Figures --- p.ix / List of Tables --- p.xii / Chapter Chapter 1 --- Background of study --- p.1 / Chapter 1.1 --- Introduction --- p.1 / Chapter 1.2 --- Theoretical background of XPS --- p.2 / Chapter 1.2.1 --- Principle of XPS --- p.2 / Chapter 1.2.2 --- Surface sensitivity --- p.6 / Chapter 1.2.3 --- Inelastic Mean Free Path (IMFP) --- p.6 / Chapter 1.3 --- XPS spectral features --- p.7 / Chapter 1.3.1 --- Chemical shift --- p.8 / Chapter 1.3.2 --- Spin orbital splitting (SOS) --- p.8 / Chapter 1.4 --- Quantitative analysis in XPS --- p.10 / Chapter 1.4.1 --- Atomic concentration --- p.10 / Chapter 1.4.2 --- Layer thickness determination --- p.11 / Chapter 1.5 --- The new XPS analysis technique in the present study --- p.14 / Chapter 1.5.1 --- Ion sputtering --- p.14 / Chapter 1.5.1.1 --- Sputtering-induced defects --- p.16 / Chapter 1.5.1.2 --- Effects of ion incident angle --- p.17 / Chapter 1.5.1.3 --- Depth resolution --- p.17 / Chapter 1.5.2 --- Perpendicular detection --- p.19 / Chapter 1.6 --- Objectives of present study --- p.23 / References for Chapter1 --- p.24 / Chapter Chapter 2 --- Instrumentation --- p.28 / Chapter 2.1 --- Introduction --- p.28 / Chapter 2.2 --- X-ray Photoelectron Spectroscopy --- p.28 / Chapter 2.2.1 --- XPS used in the present study --- p.28 / Chapter 2.2.2 --- Vacuum requirements --- p.29 / Chapter 2.2.3 --- X-ray source --- p.29 / Chapter 2.2.4 --- Charge Neutralizer --- p.33 / Chapter 2.2.5 --- Ion sputtering gun --- p.34 / Chapter 2.2.6 --- Electron energy analyzer --- p.36 / Chapter 2.2.6.1 --- Energy resolution --- p.38 / Chapter 2.2.6.2 --- Pass energy --- p.38 / Chapter 2.2.7 --- Electron detector / Multiplier --- p.39 / Chapter 2.3 --- Other analysis techniques for verification --- p.42 / Chapter 2.3.1 --- Energy Dispersive X-ray detector in Scanning Electron Microscope (SEM-EDX) --- p.42 / Chapter 2.3.2 --- X-ray Fluorescence Spectrometer (XRF) --- p.42 / Chapter 2.3.3 --- Rutherford Backscattering Spectrometer (RBS) --- p.43 / Chapter 2.3.4 --- Differential Scanning Calorimeter (DSC) --- p.44 / References for Chapter2 --- p.45 / Chapter Chapter 3 --- Determination of the thickness of the damaged layer --- p.46 / Chapter 3.1 --- Introduction --- p.46 / Chapter 3.2 --- Experimentation --- p.46 / Chapter 3.2.1 --- Instrumentation --- p.46 / Chapter 3.2.1.1 --- Work function calibration --- p.48 / Chapter 3.2.1.2 --- Sputtering ion beam calibration --- p.49 / Chapter 3.2.2 --- Sample preparation --- p.49 / Chapter 3.2.3 --- XPS measurements --- p.51 / Chapter 3.3 --- Results and discussion --- p.53 / Chapter 3.3.1 --- Spectral analysis and peak fitting --- p.53 / Chapter 3.3.2 --- Modeling and damaged layer thickness determination --- p.59 / Chapter 3.3.3 --- TRIM simulation --- p.62 / Chapter 3.4 --- Conclusion --- p.65 / References for Chapter3 --- p.68 / Chapter Chapter 4 --- Applications of the new XPS technique to different materials --- p.70 / Chapter 4.1 --- Introduction --- p.70 / Chapter 4.2 --- Analysis of ceramic --- p.70 / Chapter 4.2.1 --- Experimentation --- p.71 / Chapter 4.2.2 --- XPS results and comparison with other analysis techniques --- p.74 / Chapter 4.3 --- Analysis of metal alloys --- p.77 / Chapter 4.3.1 --- Experimentation for the tin-lead solder bump analysis --- p.78 / Chapter 4.3.2 --- Calibration of XPS sensitivity --- p.78 / Chapter 4.4 --- Development of XPS analysis method for the tin-silver solder bump measurement --- p.82 / Chapter 4.4.1 --- Experimentation --- p.83 / Chapter 4.4.2 --- XPS results --- p.83 / Chapter 4.5 --- Analysis of polymer (Polyacrylic acid) --- p.84 / Chapter 4.5.1 --- XPS results --- p.84 / Chapter 4.6 --- Analysis of Indium Phosphide --- p.90 / Chapter 4.6.1 --- XPS results --- p.92 / Chapter 4.7 --- Analysis of Gallium Arsenide --- p.96 / Chapter 4.8 --- Conclusion --- p.100 / References for Chapter4 --- p.101 / Chapter Chapter 5 --- Conclusions --- p.102

A model has been developed for calculating x-ray line emission from spherical plasmas. The main features of this method are: (1) Plasma parameters are obtained from a one-dimensional Lagrangian hydrodynamics and heat flow code. (2) Multi-frequency groups: the line structure can be reproduced with the desired accuracy by adjusting the number of frequency groups. (3) Self consistent, time dependent excited level populations and radiation fluxes: the code starts with coronal populations, calculates the ensuing radiation flux and then recalculates the populations and so on, iterating until convergence is reached. (4) Goemetrical groups of rays groups by spherical impact parameters. (5) Line broadening due to ionic thermal agitation and Doppler shift due to the net plasma flow velocity. Inclusion of the flow velocity shift would be different without the multi-frequency group treatment. The method has been applied to an aluminum target, and the results are in good agreement with previous experimental work. The total energy, summed over all lines, as well as the line intensity ratios (which are a sensitive measure of agreement with experiment) were predicted with good accuracy. The pictures that would be seen by a pinhole camera are also calculated by the code.

The objective of this project was to develop a prototype of an automated positioning system for future APXS instruments. The current instruments on Mars rely solely upon the rover arm to place them against rocks or soils, making consecutive measurements with small offsets challenging and resource intensive to conduct. The prototype consists of an x-ray detector and an x-ray tube mounted to a computer controlled three-axis positioning system. Passive surface scans were completed over 55Fe and 244Cm sources to determine raster parameters and to characterize the detector field of view. Active XRF scans of a sample tray containing geological specimens, as well as heterogeneous natural rocks, were acquired to evaluate the system under a variety of field conditions. The results demonstrate that a microcontroller, similar to that used by the APXS for signal processing, is capable of automated scanning and rudimentary decision making based on short duration spectra. This involved using the elemental distribution within the scan field to automatically position the instrument to the region of greatest scientific interest in the xy plane, and adjusting the detector stand-off for optimal data acquisition. The achievable spatial resolution was sufficient to distinguish regions of distinct elemental composition as small as 5 mm, although smaller dimensions are possible. While several aspects of the system must be developed further in order to accommodate more complex sample geometries and enable more advanced decision making, the results clearly demonstrate the potential of such a system to significantly improve the scientific return of future instruments.

Thesis (Ph.D.). / Written for the Dept. of Mining and Materials Engineering. Title from title page of PDF (viewed 2008/01/12). Includes bibliographical references.

Thesis (M.S.)--University of Missouri-Columbia, 2005. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (December 18, 2006) Includes bibliographical references.

The surface-specific analytical technique of X-ray photoelectron spectroscopy (XPS) is described, and was used to study various geochemical materials and organic compounds. Variation of surface pyrite density with coal particle size (53-250/µm) in a typical Canadian coal (Minto) provided some interesting data- it is very likely that as coal is crushed, one eventually reaches a particle size where the surface pyrite/carbon ratio maximizes. It is this parameter that is examined here, and correlations were found between (i) surface pyrite concentration,(ii) surface pyrite/sulfate ratio, and (iii) oxidized and non-oxidized sulfur with particle size. This is information which should find useful application in coal cleaning technology. For non-oxidized coal, we find the area of exposed pyrite on the coal surface is approximately inversely proportional to coal particle radius. However, for oxidized coal the appearance of curves depends on the oxidation times, but there is a particle size which exhibits maximum surface pyrite relative to 1/radius, corresponding to the intercept point of the two linear segments (low and higher values of 1/R) for the non-oxidized coal (fig. 3.9), and which is evidently that we will call the "characteristic" size of constituent pyrite. XPS 2p₃/₂ sulfur peaks from major sulfur constituents other than sulfate in sediment recovered from Mahoney Lake (south-central British Columbia, Canada) show a surprisingly periodic variation in sulfur 2p₃/₂ binding energy (BE), and hence molecular structure, with sediment age. The pattern ceases at a core depth of about 3.2 meters, where a major deposit of fine sandy sediment occurs just below ash deposition (2.6m) from a major eruption of Mount Mazama, Oregon, approximately 6500 year ago, which led to the formation of Crater Lake. Sedimental sulfur exists mainly as sulfate; however, there is a pronounced increase in amount of the lower BE sulfur species relative to sulfate toward lower depths. The "reduced" species also shows a trend towards slightly higher oxidation level at lower depths. We are able to suggest the probable chemical forms in which the sulfur species exist, which is of interest to biologists working on sulfur transformation studies in lakes. BE' s for nitrogen Is and sulfur 2p₃/₂ in the metal chelates of dibenzyldithiocarbamic acid M(DBDTC)n for n=2, M=Cu(II) and Zn(II), and for n=3, M=Bi(III), have been measured. The nature of the spectral peaks and core BE's indicates that the nitrogen atom in the DBDTC is not intramolecularly bound with the metal as had been previously suggested. The relatively high BE's for the nitrogen Is orbitals indicate planar geometry for the coordinated ligands, and the form [formula omitted] to reasonably represent their structure, which agrees with previous infrared studies. / Science, Faculty of / Chemistry, Department of / Graduate

While much is known about the toxicity of polychlorinated biphenyls (PCBs), there are tens of thousands of natural and synthetic chemicals in the environment that can activate the aryl hydrocarbon receptor (AhR) and thus cause toxicity. Since it would be difficult to conduct studies of the toxicity of each and every compound, here is presented a new model based on first-principles taking into account the basic electronic and electron trans- fer characteristics of PCBs, but can be used to predict the toxicities of other AhR-active compounds. The predictive model is based on Density Functional Theory. The model predicts that the energy gap between highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbitals is the overarching indicator of toxicity of PCBs, but not the only factor. The model explains why chlorination of both para-positions is required for maximum toxic potency. To rank potency of PCBs, the dipole moment in relation to the most chemically active chlorine-sites is critical. The theory is consistent with the accepted toxic equivalency factor (TEF) model for these molecules and is also able to improve on ranking toxic potency of PCBs with similar TEFs. This new model also includes a 13th dioxin-like PCB, PCB 74, not considered in the current TEF model developed by the World Health Organization (WHO). The model was applied to HOMO-LUMO gap mea- surements of a set of PCBs and the measurements are consistent with the model. Values of HOMO-LUMO gap can also be used to predict bio-accumulation of PCBs. The model provides an in silico method to screen a wide range of chemicals to predict their ability to act as an AhR agonist.

M.Sc., Faculty of Science, University of the Witwatersrand, 2011 / The objective of the study was to investigate the preparation of glass beads for base metal analysis of mining samples prior to x-ray fluorescence analysis. The research method used included the investigation of different fluxes, oxidising, non-wetting agents, fusion temperature and time. The experiments were carried out using different fusion instruments: Electrofluxer and Katanax followed by both EDXRF and WDXRF analysis. The x-ray spectrometers were calibrated with standards prepared from pure oxides and the results compared to values determined by alternative techniques. Different statistical methods were used to validate the experiments including factorial designs. Not all the elements and oxides were recovered successfully, however, perfect glass beads were prepared. The two areas of concern were addressed successfully: firstly the loss of copper was overcome by using an alternative heating mechanism of the Katanax and sodium iodide as the non-wetting agent. Secondly, the sulphur was successfully oxidised and retained in the glass beads.