Thesis (M. Phil.)--University of Hong Kong, 1999. / Includes bibliographical references (leaves 107-108).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1965. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Electron crystallography is powerful for determination of complex structures. The newly-developed 3D electron diffraction (ED) methods make structure determination from nano- and micron-sized crystals much easier than using other methods, for example X-ray diffraction. Almost complete 3D ED data can be collected easily and fast from crystals at any arbitrary orientations. Dynamical effects are largely reduced compared to zonal ED patterns. 3D ED is powerful for phase identification and structure solution from individual nano- and micron-sized crystals, while powder X-ray diffraction (PXRD) provides information from all phases present in the samples. 3D ED methods and PXRD are complementary and their combinations are promising for studying multiphasic samples and complicated crystal structures. In this thesis, the feasibility and capability of 3D ED methods, specifically rotation electron diffraction (RED), in phase identification and structure determination of different kinds of crystalline materials with nano- or submicrometer-sized crystals are investigated. Experimental conditions for RED data collection and data processing in relation to data quality, as well as the challenges in the applications of RED are discussed. RED was combined with PXRD to identify phases from as-synthesized samples and to characterize atomic structures of eleven crystalline compounds. It was shown to be possible to identify as many as four distinct compounds within one sample containing submicron-sized crystals in a Ni-Se-O-Cl system. RED was also used to determine unit cell and symmetry of isoreticular metal-organic frameworks (SUMOF-7) and solve five zeolite structures with new frameworks, ITQ-51, ITQ-53, ITQ-54, EMM-23 and EMM-25 and that of a metal-organic framework (MOF), SUMOF-7I. The structure of an open-framework germanate SU-77 was solved by combining RED with PXRD. The structures of the zeolites and SU-77 were confirmed by Rietveld refinement against PXRD. High-resolution transmission electron microscopy was used to confirm the structure models of ITQ-51, EMM-25 and SUMOF-7I. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 4: Accepted. Paper 6: Manuscript. Paper 7: Epub ahead of print. Paper 9: Manuscript. Paper 11: Manuscript.</p>

Electron crystallography has been proven to be effective for structure determination of nano- and micron-sized crystals. In the past few years, 3D electron diffraction (3DED) techniques were used for the structure solution of various types of complex structures such as zeolites, metal-organic frameworks (MOF) and pharmaceutical compounds. However, unlike X-ray crystallography, electron diffraction has not yet become an independent technique for a complete structure determination due to relatively poorer diffraction intensities and often powder X-ray diffraction data are used for structure validation and refinement. Electron beam damage to the structures that are sensitive to high energy electrons and dynamical scattering are important factors to lead to the deviation of electron diffraction intensities from the squared amplitudes of the structure factors. In this thesis, we investigate various aspects around the 3D electron diffraction data quality and strategies for obtaining better data and structure models. We combined 3D electron diffraction methods and powder X-ray diffraction to determine the structure of an open-framework material and discussed the difficulties and limitations of electron diffraction for beam sensitive materials. Next, we illustrated the structure determination of a pharmaceutical compound, bismuth subgallate, using 3D electron diffraction. While severe beam damage and diffuse scattering were observed in the dataset collected with the conventional rotation electron diffraction (RED) method, the continuous rotation electron diffraction (cRED) method coupled with sample cooling significantly improved the data quality and made the structure solution possible. In order to better understand the potentials and limitations of the continuous rotation method, we collected multiple datasets from different crystals of a known structure and studied the data quality by evaluating the accuracy of the refined structure models. To tackle dynamical scattering in electron diffraction data, we explored a routine for structure refinement with dynamical intensity calculation using RED data from a known structure and discussed its potentials and limitations. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.</p>

published_or_final_version / abstract / toc / Physics / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Physics / Doctoral / Doctor of Philosophy

No description available.

For the past 75 years gas-phase electron diffraction (GED) has remained the most valuable technique for determining structures of small molecules, free from intermolecular interactions. Throughout this period many improvements have been made to both the experimental and theoretical aspects of this technique, leading to the determination of more accurate structures. As the uncertainties associated with many stages of the process have been greatly reduced, errors introduced by assumptions, which were previously neglected, now play an important role in the overall accuracy of the determined structure. This work is focused on two such areas, namely the treatment of vibrational corrections and the vibrational effects on the scattering of individual electrons by multiple atoms. A novel method has been developed which allows the extraction of equilibrium structures (re) from distances obtained directly from GED experiments (ra). In unfavourable cases (such as small molecules with large-amplitude and / or highly anharmonic modes of vibration) traditional methods can introduce errors of comparable size to those obtained from the experiment. The newly developed method, EXPRESS (EXPeriments Resulting in Equilibrium StructureS), overcomes the problems which have plagued previous attempts through exploring a more extensive region of the potential-energy surface (PES), specifically regions relating to the normal modes of vibration. The method has been applied, initially, to sodium chloride in the gas phase as this contains dimer molecules with very low-frequency large-amplitude modes of vibration. The experimentally determined re structure gives good agreement with high-level ab initio calculations. Following this success, the EXPRESS method was then applied to sodium fluoride, sodium bromide and sodium iodide, giving similarly good agreement with theoretical calculations. The regular mixed alkali halide dimers (D2h symmetry) cannot be studied by microwave spectroscopy as they do not have a permanent dipole moment. However, vi mixed dimers (C2v) and asymmetric dimers (Cs) do not suffer from this constraint. Using insights learned from the ab initio studies of the sodium halides, geometries and dipole moments have been calculated for a range of mixed and asymmetric alkali halide dimers to enable their study by microwave spectroscopy. A multi-dimensional version of the EXPRESS method has been applied to the lowfrequency modes of chlorofluoroacetylene and chlorodifluoronitrosomethane to assess the effects of coupling between these modes of vibration in these structurally challenging systems. To obtain re structures of larger molecules a second method, using molecular dynamics (MD), has been developed and has been implemented on two test cases: the sodium chloride dimer and octasilsesquioxane. Traditional scattering theory used in GED employs the first-order Born approximation (FBO). However, this ignores any multiple scattering events, which are important for heavier atoms. Using a method similar in nature to EXPRESS a full vibrational analysis of three-atom scattering has been conducted on tellurium dibromide and tellurium tetrabromide.

Xu Xiangdong. / "December 2001." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2001. / 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. / Abstracts in English and Chinese.

The interactions of a model synthetic liquid fuel reactant (furan) with a model hydrodeoxygenation catalyst (clean and sulfided single crystal molybdenum) were investigated using the following UHV tools: Auger electron spectroscopy (AES), low energy electron diffraction (LEED), and temperature programed reaction spectroscopy (TPRS). In addition to furan, the reactions of hydrogen, carbon monoxide, ethylene, and propene on clean and sulfided Mo(110) were also examined. All adsorbates exposed to the extremely reactive clean or sulfided Mo(110) surface decomposed, yielding gaseous H��� and surface C. In addition, furan TPRS caused the production of gaseous CO. The presence of background hydrogen caused no major changes in the TPRS of furan or the other adsorbates. Sulfur pre-adsorption caused the chemical shifting of H��� TPRS peaks. Both sulfur and carbon pre-adsorption resulted in the Van der Waal's radius blocking of adsorption sites for all adsorbates studied. / Graduation date: 1997