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

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.

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.

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Unique physical properties such as small effective mass, high electron drift velocities, high electron mobility and small band gap energy make InN a candidate for applications in high-speed microelectronic and optoelectronic devices. The aim of this research is to understand the surface properties, desorption kinetics and thermal stability of InN epilayers that affect the growth processes and determine film quality as well as device performance and life time. We have investigated the structural properties, the surface desorption kinetics, and the thermal stability using Auger electron spectroscopy (AES), x-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), high resolution electron energy loss spectroscopy (HREELS), and temperature programmed desorption (TPD). Investigations on high pressure chemical vapor deposition (HPCVD)-grown InN samples revealed the presence of tilted crystallites, which were attributed to high group V/III flux ratio and lattice mismatch. A study of the thermal stability of HPCVD-grown InN epilayers revealed that the activation energy for nitrogen desorption was 1.6±0.2 eV, independent of the group V/III flux ratio. Initial investigations on the ternary alloy In0.96Ga0.04N showed single-phase, N-polar epilayers using XRD and HREELS, while a thermal desorption study revealed an activation energy for nitrogen desorption of 1.14 ± 0.06 eV. HREELS investigations of atomic layer epitaxy (ALE)-grown InN revealed vibrational modes assigned to N-N vibrations. The atomic hydrogen cleaned InN surface also exhibited modes assigned to surface N-H without showing In-H species, which indicated N-polar InN. Complete desorption of hydrogen from the InN surface was best described by the first-order desorption kinetics with an activation energy of 0.88 ± 0.06 eV and pre-exponential factor of (1.5 ± 0.5) ×105 s-1. Overall, we have used a number of techniques to characterize the structure, surface bonding configuration, thermal stability and hydrogen desorption kinetics of InN and In0.96Ga0.04N epilayers grown by HPCVD and ALE. High group V/III precursors ratio and lattice mismatch have a crucial influence on the film orientation. The effects of hydrogen on the decomposition add to the wide variation in the activation energy of nitrogen desorption. Presence of surface defects lowers the activation energy for hydrogen desorption from the surface.

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This thesis is comprised of two closely related studies of fullerenes. The first part is an investigation of C60 and C70 nanocrystals using both experimental and simulated electron energy loss (EEL) spectra. Through a detailed comparison of particular features in EEL spectra collected from these materials in a transmission electron microscope, with simulated spectra, it is established that differences in spectra from different materials can be linked to particular aspects of the structural models. For example, in the case of C60 differences in experimental spectra from different samples can be linked to differences in the bond lengths within the molecules of different samples. In the case of C70, it is found that features within the spectrum which have previously been attributed to the ten equatorial atoms do not have this origin in a crystal. The second part is an experimental investigation of endohedral fullerenes Nd@C82 and Sc3N@C80. The effect of temperature on the EEL spectrum is investigated and, in the case of Nd@C82, the effect of the presence of different isomers is also investigated. Spectra are successfully obtained from the encapsulated atoms, and the importance of careful experiments in terms of avoiding contamination is highlighted.

This thesis explores the theory describing wavefunctions and images, both elastic and inelastic, formed in scanning transmission electron microscopy. / A method is presented for calculating the elastic wavefunction based upon a new formulation of the boundary conditions which couples the probe to Bloch states within the crystal in a single step. Though this method is fundamentally equivalent to previous approaches based upon the superposition of wavefunctions corresponding to individual plane wave components in the incident probe, it provides new insight into the some of the dynamics, allows for efficient calculations, and proves useful for demonstrating well known results such as reciprocity relations. A formal inversion technique is also presented that uses a collection of diffraction plane data in scanning transmission electron microscopy to reconstruct the object potential, even in the presence of strong multiple scattering. / The new form of the boundary conditions allows for a generalization of a crosssection expression for calculating inelastic images, making use of the theory of mixed dynamic form factors. This enables the simulation of images for a range of inelastic mechanisms, including thermal scattering, used to simulate high-angle annular dark field imaging, and inner-shell ionization, used to simulate electron energy loss spectroscopy images. A multislice form of this expression is given. Selection between the methods can thus be based on the sample of interest: the Bloch wave method is very efficient when the sample is crystalline; the multislice method is more appropriate if the sample lacks periodicity. / The issue of cross-talk, where dynamical probe spreading may result in a signal containing contributions from several columns and therefore confound direct interpretation, is assessed for high-angle annular dark field imaging. Single atom images are simulated to provide an estimate of the localization of signal in electron energy loss spectroscopy, and confirm that the limitations of probe size generally outweigh those of the nature of the ionization interaction. The feasibility of column-by-column spectroscopic identification is demonstrated through a combination of experimental data and supporting calculations. Data demonstrating the location and spectroscopic identification of a single impurity atom in the bulk are supported by simulation and it is demonstrated that a quantitative comparison can offer further useful information: an estimate for the depth of the impurity. / The contribution to electron energy loss spectroscopy images from electrons which have undergone thermal scattering prior to causing an inner-shell ionization event is assessed. It is concluded that this contribution is significant in strongly scattering specimens imaged using fine probes. It will be necessary to include this contribution if quantitative comparisons are to be made.

This thesis explores the theory of electron energy-loss spectroscopy (EELS) in atomic resolution electron microscopy. / The first unequivocal evidence of the effective nonlocal potential in momentum-transfer-resolved EELS is presented. For suitable geometries, the nonlocal potential can be well approximated by a local potential. In scanning transmission electron microscopy (STEM) the validity of this is mainly influenced by the detector size and, contrary to conventional wisdom, a thin annular detector does not allow direct image interpretation. It is found that the best way to ensure the potential is well approximated by a local potential is to use a detector with a large collection angle. / To simplify computation and interpretation it is desirable to make the single-channelling approximation. In this approximation only the elastic scattering of the probe before the ionisation event is modelled. It is shown how this approximation breaks down for the small detectors used in momentum-transfer-resolved EELS and this is confirmed with experimental results. Double-channelling calculations, where the channelling of the probe both before and after the ionisation event are modelled, can also be simulated. An alternative approximation for small detectors that includes double channelling and is more applicable for momentum-transfer-resolved EELS is also presented. / Beyond chemical information, the fine structure of an absorption edge gives bonding and electronic information. Incorporating fine structure into channelling theory allows the exploration of the effects of channelling on fine structure. The weighting of the two different spectra in graphite, as a function of incident probe tilt in momentum-transfer-resolved EELS, is calculated using double-channelling simulations. This is combined with experimental data and multivariate statistical analysis to extract the two physical spectra, greatly simplifying the analysis of a large data set. / The effect of the nonlocal potential and channelling on site-specific electronic structure analysis by channelling EELS is examined. It is found that using a large on-axis detector can make the interaction effectively local, leading to a greater change in the spectra as a function of sample tilt. Alternatively offsetting the detector can achieve similar results but at the cost of greater statistical noise. Channelling calculations were combined with the program FEFF and the full energy differential cross section was calculated from first principles for the aluminium K edge as a function of sample tilt in nickel aluminate spinel. Qualitative agreement with experiment was found but quantitative agreement will require further investigation. / The theory of fine structure in STEM was examined, using strontium titanate to see how the high spatial resolution of STEM can be used in conjunction with energy-loss near-edge spectroscopy measurements. The possibility of imaging unoccupied electron molecular orbitals using STEM was also examined.