by Ka Wai Wong. / "June 1999." / Thesis (Ph.D.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / by Ka Wai Wong.

Thesis. 1975. Sc.D.--Massachusetts Institute of Technology. Dept. of Mechanical Engineering. / Vita. / Bibliography: leaves 82-84. / Sc.D.

Ge(100) has atomic and electronic structures quite similar to those of Si(100). As a comparison, we have studied the oxidation of Ge(100) surface. Our comparison of the initial oxidation of Ge(100) with that of Si(100) by molecular oxygen shows that the precursor-mediate mechanism and direct adsorption mechanism are common to both systems. (Abstract shortened by UMI.) / It is often been argued that a direct [2+2] addition of unsaturated hydrocarbons to the Si-Si dimer is symmetry forbidden, according to the Woodward-Hoffmann rule. This view is now challenged by our calculations on the reaction path for a concerted [2+2] addition of C2H4 to a Si-Si dimer on Si(100), which identifies a barrier of only ∼0.1eV. Our analysis shows that this is due to the peculiar feature for a surface reaction, when the HOMO and LUMO bands cross the Fermi level of the substrate, as previously suggested by Hoffmann. It illustrates an important conceptual distinction between a gas phase and a surface reaction. / Many previous theoretical studies on the interaction between O2 and Si(100) have neglected the differences between triplet O2 (ground state) and singlet O2 (excited state), and are thus unable to explain the know experimental observations in surface scattering of O2. We demonstrate that in reality, triplet O2 can also react with Si(100). With our computation results on the potential energy curves of the adsorption of triplet O2 on Si(100) and the adsorption structures along these curves, we can explain the known experimental results. The proper adsorption pathway goes through a shallow physisorption potential well, a small transition state and reaches a molecular adsorption state. There are also some interesting interactions between the potential energy curves of the triplet O2 adsorption and singlet O2 adsorption. / This thesis addresses the basic physics and chemistry of some surface reactions by first-principles methods based on density functional theory. The reaction systems probed by this thesis include the cycloaddition of C2H4 on Si(100), and initial oxidation of Si(100), Ge(100) and Al(111) by molecular oxygen. They are all technologically important systems and yet simple enough for us to study them in details theoretically. Although they have been studied both experimentally and theoretically, our first principles calculations reveal new insights that are contrary to prevalent opinions. / Fan Xiaoli = 从头算法研究研究在硅100, 锗100 和铝111 表面上的反应 / 范晓丽. / "June 2005." / Adviser: Lau Woon-ming Leo. / Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 3854. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Text in English; abstracts in English and Chinese. / School code: 1307. / Fan Xiaoli = Cong tou suan fa yan jiu yan jiu zai gui 100, zhe 100 he lü111 biao mian shang de fan ying / Fan Xiaoli.

Styrene (C2H3-C6H5) is expected to have a more complex reaction process due to active reaction sites located in both vinyl group and phenyl group. Our exploration indicates that the adsorption products are coverage dependent. At low coverage, both vinyl group and phenyl group are possible to take part in the adsorption process. A new AsymT adsorption state covered two adjacent Si dimers is identified through two [4+2] cycloaddition. At high coverage, only vinyl group can interact with Si dimer to form cis and trans stereoisomers with different thermal energies and kinetic reaction barriers. STM images and vibrational frequencies are also explored to further support the experimental observations. / The adsorption of unsaturated organic molecules on reconstructed Si(100) surface is widely applied in the modification and functionalization of silicon surface to design new semiconductor materials. The present project is devoted to explore the adsorption mechanisms and the related properties of adsorption species for unsaturated organic molecules: acetylene (C2H 2), ethylene (C2H4), vinyl bromide (C2H 3Br) and styrene (C8H8) by quantum chemical calculation, based on density functional theory (DFT) method with pseudopotentials and plane wave basis set. / The investigation of vinyl bromide (C2H3Br) chemisorption on Si(100) resolves the conflicting conclusions between previous experimental and theoretical studies. The orientation of the vinyl bromide molecule relative to the titled silicon dimer is found to be an important factor for both the stability and reactivity of the precursor state. A new precursor pi-complex is identified, which is metastable and trapped by barriers around 0.1eV. Comparisons between theoretical and experimental vibrational frequencies support the conclusion that such a pi-complex is present on the surface at very low temperature. Careful analysis on the electronic structure also demonstrates that it is indeed a pi-complex rather than a diradical as previously suggested. Reaction mechanisms at higher vinyl bromide coverage are also modeled to explain the decrease in activation barrier observed in experiments. / The reaction processes for acetylene (C2H2) and ethylene (C2H4) chemisorption on the surface silicon dimer and the sub-layer silicon atoms are compared. Acetylene can undergo a new type of cycloaddition on sub-layer Si atoms (called sub-di-sigma) with no barrier, which is identified by ab initio Molecular Dynamics. The related properties including vibrational frequencies and STM images are calculated and found to be similar with those of the end-bridge adsorption structure. The identification of such a sub-di-sigma adsorption structure explains the discrepancy between STM experiments and theoretical calculations. In addition, the analysis of calculated vibrational frequencies, simulated STM images and the reaction barriers for di-sigma and end-bridge structures indicate that inter-dimer reaction for C2H4 is possible. / Zhang, Qiuji. / Adviser: Zhi Feng Liu. / Source: Dissertation Abstracts International, Volume: 70-09, Section: B, page: . / Thesis submitted in: October 2008. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 86-87). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

The aim of the research presented in this thesis was to increase the understanding of the interaction between polymeric dispersants and titania pigment particles. In particular, the effects of dispersants of varied functionalities on the pigment dispersion behaviour in both aqueous suspension and dry paint film were investigated. / thesis (PhDEng(MineralsandMaterials))--University of South Australia, 2004.

Polystyrenes with carboxyl end-groups (PS-COOH)and poly (tert-butyl acrylates) (PtBA) of different molar mass were synthesised by anionic polymerisation using n-butyllithium as the initiator. Gel permeation chromatography (GPC) was used to calculate the molecular weight and polydispersity of these polymers. The tacticity of these polymers was determined using Carbon 13 Nuclear Magnetic Resonance Spectroscopy (13C NMR). FT-IR was used to confirm the tacticity of the samples. Matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF) was used to confirm the presence of the carboxyl end-groups. All of the films studied in this project were transferred to mica substrates using the Langmuir-Blodgett deposition method. Both single layer and multiple layer films were constructed using this technique. Atomic force microscopy (AFM) was used to observe the surface topology of these films. / Doctor of Philosophy (PhD) (Science)

In order to clarify the role that water plays in the photocatalytic process, changes in the IR and Raman spectra of P25 TiO₂ thin films were observed upon exposure to liquid water. Further investigation of these spectral changes via dehydration of thin films under nitrogen and oxygen of different humidities led to the observation of spectroscopic features that have been assigned to localised surface phonon modes. When the effect of UV irradiation on these features was investigated, a broad IR absorption due to transitions of electrons in shallow traps was detected under dry nitrogen but not under dry oxygen. Further investigation of the photocatalytic properties of P25 TiO₂ showed a complete removal of a stearic acid film. The final products have been tentatively assigned to a mixture of short chain carbonyl species and adsorbed carbonates as well as carbon dioxide and water. The IR spectrum of the fuel cell membrane material Nafion is complex and literature data varies in some of the assignments. The compound perfluoro(2-ethoxyethane)sulfonic acid was used as a model compound for the Nafion side chain resulting in a clearer assignment of the Nafion IR spectrum. In light of these new assignments changes induced in the region 1100-1300 cm⁻� by variation in humidity and ion exchange have been shown to be mainly the result of changes in the sulfonate asymmetric stretching modes. By flowing a series of solutions containing tetramethylammonium ions and perchlorate ions the surface charge characteristics of a Pt black film were determined in the pH range 2-12. There proved to be a weak positive charge below pH 4 and a weak negative charge above pH 9. Between these points there appeared to be no overall charge on the surface. When perfluoro(2-ethoxyethane)sulfonic acid was adsorbed to a Pt black film changes in its IR spectrum indicated a strong binding via interactions between the sulfonate groups and the Pt surface. The nature of the adsorption of Nafion was less clear cut and, whilst adsorption is strong, it seems possible that hydrophobic interactions between the Nafion backbone and the surface are involved.

This thesis presents: 1) literature review on adhesive bonding technologies in aviation industry including surface pretreatments (pre-preparation), surface quality assurance, and surface chemistry analysis methods; and 2) development and study of a novel solid-state electrochemical sensor for surface chemistry analysis of composite surfaces. The performance of an adhesive bonding is greatly determined by the adherend?s surface pretreatments which could increase surface tension, surface roughness, and change surface chemistry thereby increasing bond strength and durability of polymer composite adhesive joints. The primary goal of the surface pretreatments is to increase the surface roughness, surface energy, chemical activity, and cleanliness of the composite adherend as much as possible. Methods of surface pretreatments are reviewed in this paper, including: (1) abrasion/solvent cleaning; (2) grit blasting; (3) peel-ply; (4) tear-ply; (5) acid etching/anodizing; (6) corona discharge treatment; (7) plasma treatment; (8) flame treatment; (9) laser treatment; (10) others. One of the critical issues in aviation industry for an adhesive bonding is to analyze the prepared composite surfaces using a nondestructive inspection (NDI) or nondestructive test (NDT) method to determine whether the quality of surfaces are ready for the following bonding processes. Existing NDI methods include: (1) Near-Infrared; (2) Electrical potential; (3) Transient thermal NDT; (4) Electrical Impedance Spectroscopy (EIS); (5) Neutron radiography; and (6) X-ray Photoelectron Spectroscopy (XPS). However, up till now, these methods cannot provide definitive analysis or online and in-field analysis. Because of the non-availability of an on-line, in-field NDI method for surface chemistry analysis, excess or inadequate surface treatment and quality control processes may exist in the current aircraft manufacture processes incurring either a high cost or potentially weak adhesive bonds. Electrochemical reactions usually occur in liquid electrolyte or on conducting electrode but not on non-conducting composite. Conventional electrochemical sensors involve liquid electrolytes which will cause contamination on composite surfaces when they are used for surface chemistry analysis. In this work, we explore an all solid-sate electrochemical sensor technology. Redox pairs or mediators are combined into a solid-state electrolyte, NafionTM. The mediators can pass electrons to or from the composite surfaces causing slight reduction or oxidation of the composite surfaces. The output current in response to cyclic polarization (cyclic potential scanning) is used as the indication of the surface contamination level. The sensors included a working or sensing electrode with mediated Nafion clusters, Nafion membrane, Pt catalyzed carbon counter electrode, and Ag|AgCl reference electrode. The working electrode and counter electrode were attached to the Nafion membrane from different sides. The sensors were tested on different kinds of surfaces: original, polished, and sulfuric acid treated acrylic samples and pristine peel ply prepared, polished, and sulfuric acid treated composite laminate surface samples. The sensors showed a high sensitivity to the surface contamination. The performances and possible mechanisms related to the electrochemical sensors are discussed.

Adsorption at metal electrodes is usually a very fast process and it plays a most important role in many areas of industry. The thermodynamics of the process are well known for many systems. However, there is currently no good method that allows a determination of very fast kinetics of adsorption to be made. Previously, many attempts at evaluation of kinetic parameters of adsorption were made, but in moat cases, due to the inadequacy of the experimental methods used, the parameters obtained were much lower than expected. This thesis aims at providing the means for determining the kinetics of adsorption at metal electrodes. The methods herein described are based on two different experimental techniques. These techniques are: (i) fast cyclic voltammetry (FCV, potential sweep rate up to 100000 V/s) and (ii) high frequency AC and FFT SW (Fast Fourier Transform Square-wave) voltammetry (frequency up to 50 MHz) at ultramicroelectrodes (5 or 6.25 ìm in radius). A theoretical description of the adsorption process for both kinds of experiments is presented. A simulation program was written to provide a better understanding of the process and to elucidate the development of methods for determining the kinetics of adsorption. Thermodynamic and kinetic descriptions of the process are based on the Frumkin adsorption isotherm. Both the equilibrium constant and the adsorption rate constant are treated as functions of potential and the electrode coverage. Comparison of results for different systems is presented as an analysis of the dependence of the adsorption rate constant on the equilibrium constant. FCV proved to be useful in the evaluation of kinetics of chemisorption (standard rate constant in the range of 10⁶ s$\sp{-1})$ but the results for adsorption of aliphatic alcohols were unreliable. High frequency AC methods allowed the determination of kinetics of physical adsorption. It was found that the activation energy of the adsorption process can be expressed as a linear combination of the electrical component of the standard free energy of adsorption (a major contribution) and the energy of lateral interactions (a minor contribution). At the zero charge potential the rate constant reaches the maximum value of $\rm(4.6\pm0.3)10\sp9\ s\sp{-1}.$

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 167-175). Available also in a digital version from Dissertation Abstracts.