| This dissertation focuses on the development of "in-situ" environmental - transmission electron microscope (TEM) specimen holder assemblies. To date, experimentation with TEM has essentially been two-dimensional and static. In-situ experiments are presently not possible for analyzing complex hot deformation, dynamic recovery and dynamic recrystallization processes because of limitations in the specimen holder design. By developing technology that allows in-situ TEM, it will be possible to assess phenomena such as materials microstructural changes throughout heating process rather than using traditional post mortem techniques. The ability to conduct environmental in-situ experiments is also important because many biological applications currently analyze catalyst samples under static, post-reaction conditions that do not adequately represent reaction dynamics. The lack of an ability to perform in-situ analysis has delayed the fundamental understanding of dynamic catalytic surfaces, complex structural changes, and reaction mechanisms that evolve during processes such as oxidation-reduction. In this respect, this dissertation present novel holder technology that enables in-situ experiments for dynamically capturing microstructure and texture changes in specimens. Such analyses are not capable at the present time and will lead to breakthrough technologies for evaluating mechanisms of microstructural evolution and chemical process reactions.; Environmental instability has been shown to be the limiting factor in holder design when attempting to obtain TEM atomic resolution. In this dissertation, two of the most common environmental problems associated with TEM resolution have been analyzed, air pressure and temperature fluctuations. The present approach to solving these limitations has included extensive experimental and numerical analyses. Based on these analyses, we have designed and optimized two heated TEM holders that overcome the current technical problems associated with performing in situ experiments. These novel holder designs are dynamically stable and accurate for image processing, are capable of elevating the sample temperature to 2000 K, allow the specimens to be subject to diverse environments, and have minimum drift in sample position over time.; Our initial work utilized the finite element method to dynamically and thermally analyze presently available TEM holder assemblies. From these simulations, the dynamic and thermal behavior of the holders were obtained. This information proved to be critical for establishing the limitations of the present TEM technology. It also allowed creation of optimization objectives for designing holders for in-situ TEM experiments. Utilizing the numerical results of the current TEM holders as a basis, two novel different holder technologies were designed and numerically analyzed. (Abstract shortened by UMI.)... |
