Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

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At its primary level (nm scale) bone is a nanocomposite consisting of a mineral (hydroxyapatite) phase which gives bone its strength and an organic (type I collagen) phase giving bone its fracture toughness. Hydroxyapatite, (HAP) Ca10(PO4)6(OH)2, is the most abundant mineral in the human body. Bone tissue has a complex hierarchical structure spanning multiple length scales (cm to nm). Characterization of mineral composition in biomineralized tissues such as bone at their primary level, is very challenging and requires instrumentation with nanometer-scale spatial resolution. Transmission electron microscopy (TEM) combines high spatial resolution with visual correlation of diffraction and elemental-composition data. Electron energy-loss spectroscopy (EELS) is a sensitive technique used to probe electronic structure at the molecular level. TEM-based EELS is the only available technique that can provide information about the chemical and coordination environment of minerals with nm scale spatial resolution. Prior studies in our group has developed a method to create biomimetic HAP using biomineralization routes inside the clay galleries of montmorillonite clay modified with amino acids (in-situ HAPclay). Incorporation of in-situ HAPclay into polymer scaffolds and seeding with human mesenchymal stem cells has enabled the cells towards differentiation into osteoblastic lineages without differentiating media. Because of the importance of these materials for bioengineering applications, TEM-EELS was used to evaluate differences and similarities among HAP, biomimetic in-situ HAPclay, modified MMT clay, and β-tricalcium phosphate. Osteogenesis imperfecta (OI), also known as brittle bone disease, is an inheritable disease characterized by increased bone fragility, low bone mass, and bone deformity caused primarily by mutation in collagen type I genes and is expressed as changes in structure and mechanics at the macrostructural level of bone. Therefore the mineralization of HAP in OI bone and the molecular basis of OI bone disease makes this an interesting system for molecular-level investigations. Small changes in the valence band and outer electronic structures of the diseased bone have been revealed through EELS. These small changes observed in the electron energy-loss spectra of the OI bone appear to play important biological roles towards development of the disease. / National Science Foundation under Grant Nos. 0619098, 0821655, 0923354, and 1229417

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A high energy resolution transmission electron energy loss spectrometer was reassembled for this research project. The vacuum system, electron optical lenses, electronic control elements, and high voltage system were reconditioned. A CAMAC interface system was installed into the spectrometer, and a data collecting software package was developed which included a direct convolution method for removing the contributions of multiple scattering from the data. The spectrometer is running very well. Samples can be changed routinely without disturbing the performance of the spectrometer. The research conducted for this thesis was an investigation of the optical properties of the high temperature superconductors of Bi₂Sr₂Ca_{n - 1}Cu_nO₃(n = 1,2) by transmission electron energy loss spectroscopy. A thin film of Bi₂Sr₂CaCu₂O₈ was prepared by the flux method. A single crystal of Bi₂Sr₂CuO₆ also was grown from which a self-supporting thin film was prepared. The energy loss spectra of Bi₂Sr₂CaCu₂O₈ and Bi₂Sr₂CuO₆ materials were investigated, and the dielectric functions of these materials were derived by Kramers-Kronig analysis. A broad excitation centered at 2.7eV was identified as associated with the Cu — O₂ layer by comparing the spectrum of Bi₂Sr₂CaCu₂O₈ with that of Bi₂Sr₂CuO₆. A pseudo gap of 1.2eV in the spectrum of Bi₂Sr₂CuO₆ suggests that the one electron approximation for states derived from the hybridization of O 2p_σ and Cu3d_{x² - y²} orbital might not be valid. Two excitations at 3.6eV and 4.6eV were observed in both spectra. Comparing the spectrum of Bi₂Sr₂CaCu₂O₈ with that of Bi₂Sr₂CuO₆ suggests that the 3.6eV excitation is associated with the Bi — O layer. It was concluded that the 3.6eV and 4.6eV excitation are a spin-orbit doublet derived from the atomic bismuth 6p level. This identification is based on a comparison of Bi core level excitations from electron energy loss spectroscopy with X-ray photoemission measurements. A simplified atomic energy level picture of Bi in Bi₂Sr₂Ca_{n - 1}Cu_nO₃(n = 1, 2) is presented. A 1.0eV excitation in the energy loss spectrum of Bi₂Sr₂CaCu₂O₈ was observed, and its dispersion relationship with the momentum transfer q is presented. A Drude model was used to describe this controversial excitation. / Ph. D.

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Yuen Yung Hui. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2002. / 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 Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese. / Yuen Yung Hui.

As another important features in VEELS, the plasmon excitations (including the volume plasmon and surface/interfacial plasmon) are also utilized to identify different phases and multi compositions within materials. The microstructure and electronic structure evolution of silicon-rich oxide (SRO) films as a function of the annealing temperature are investigated using TEM and VEELS. The as-deposited SiO film is found to be a single phase with only single volume plasmon presents in VEEL spectrum and almost no interfacial plasmon is observed. After the annealing (Tanneal>400°C), it begins to decomposite into Si and SiO2 and the single phase changed into cluster/matrix nanocomposites where the interfacial plasmon appears. The Si duster size and its concentration increase as the annealing temperature increases. / Firstly, the applications of VEELS in investigating the electronic structures of ZnO nanowires with different diameter and surface shapes are demonstrated. Using the momentum transferred technique, one of the interband transitions with dipole-forbidden nature is identified. Several size dependent features are found on the interband transitions and plasmon oscillations of ZnO nanowires with small diameter and circular cross section, which are mainly due to the large surface to volume ratio and existence of Oxygen dangling bonds on those ZnO wires. / Further explorations on the electronic structure in the vicinity of band gap are carried out for the ZnO nanowires doped with different dopants (Co, Er, Yb) and different dopant concentrations. In order to obtain trustworthy information in the very low energy range of VEELS a narrow zero loss peak and elimination of Cerenkov effect and surface losses are necessary, which can be realized by incorporation of the gun monochromator in the TEM and taking spectrum at a momentum transfer slightly greater than zero. Band tail states (∼2-3.3 eV) are found to be generated in the ZnO nanowires after the ion implantation and their density of states increase with the ion fluence increases. The partially removal of those defect states by the Oxygen annealing is also observed in VEELS. On the other hand, interesting mid-gap state(s), which is dopant-sensitive (as it is only observed in the rare earth (Er and Yb) doped ZnO nanowires, but not in the Co-doped ones), does not show obvious change after the O annealing. The impact of these electronic structure changes on the material properties are also discussed. / In the end of the thesis, some of the practical limitations and contradictories on the energy resolution (DeltaE), spatial resolution (Delta x), and the momentum resolution (Deltaq) when carrying out the various VEELS study are summarized. The compromise made among these resolution limits is also discussed. / In this work, the important experimental parameters and appropriate data processing methods to generate trustworthy data are discussed. Based on that, three material systems, i.e., pure ZnO nanowires, doped ZnO nanowires, and Si/SiO/SiO2 composite films are investigated. Various information on the material microstructure/electronic structure is interpreted using the VEELS data. / The valence-electron energy-loss spectroscopy (VEELS) contains information on the electronic structures of materials, including the band gap the single-electron interband transitions and the plasmon oscillations. When operating in transmission electron microscope (TEM), the excellent spatial resolution enables the VEELS not only exploring the local electronic structures of individual low dimensional nanostructured materials, but also building up correlations between the electronic structure and microstructure. In addition, the capability in carrying out the momentum transfer dependent study in VEELS allows the investigation on the dispersion of plasmons and single electron excitations in the momentum space. The optically forbidden transitions, which are not allowed in conventional optical method, can also be excited at high momentum transfer values using VEELS. / Wang, Juan = 價電子能量損失譜在低維納米材料中的應用 / 王娟. / "September 2007." / Adviser: Li Quan. / Source: Dissertation Abstracts International, Volume: 69-02, Section: B, page: 1267. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (p. 122-133). / 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. / Abstract in English and Chinese. / School code: 1307. / Wang, Juan = Jia dian zi neng liang sun shi pu zai di wei na mi cai liao zhong de ying yong / Wang Juan.

This investigation is primarily concerned with the low loss, or plasmon region of an electron energy loss spectrum. Specifically, why these spectra have the shape and form that they do; what the significance of the material is in determining the shape and form of these spectra; what can be done with plasmon excited electrons; and how all of this fits in with the current theory of plasmon excitation. In particular, the concept of plasmon scattering being an energy transfer process of a coupled wave in the material is explored. This gives rise to slightly different explanations of the plasmon scattering process to the status quo. Multiple scattering is typically pictured as a combination of separate and independent, elastic and inelastic scattering events interactively contributing to a final exit wave function. However, this investigation explores the idea of the elastic and inelastic components being a coupled event, and what the consequences of this idea are from a conceptual point of view. The energy transfer process itself, does not deviate from a virtual particle exchange description that is consistent with the standard model. However, the two significant points made throughout the chapters are one: that the elastic and inelastic scattering events are coupled rather than separate, and two: that each succussive higher order scattering event in multiple scattering scenarios, are dependant and connecte d rather than independent.

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