Chemical and Biomolecular Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2751
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Item Interface Broadening and Radiation Enhanced Diffusion During Sputter Depth Profiling(1988) Chambers, George Paul; Rousch, Marvin; Chemical and Nuclear Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)The process of ion bombardment of solids has been investigated using Monte Carlo Computer Code simulation in conjunction with ultra-high vacuum experimental techniques. The computer code EVOLVE has been used to study the shape of the resultant collision cascade as well as the origins of sputtered particles while experimental studies of interface regions have been performed to elucidate the physical processes occurring during sputtering. The EVOLVE code models the target as an amorphous multicomponent semi-infinite solid. The target composition during ion bombardment is simulated. The study concludes that recoil activity grows in size and tends to move away from the target surface with increasing time. It is further concluded that the majority of sputtered atoms originate from early generations and are produced from sites near the entry point of the bombarding ion. Low energy noble gas ion bombardment of thin-film Cr/Ni multilayered structures has been performed in conjunction with Auger electron spectroscopy under UHV conditions. An accurate, reliable, and systematic parameterization of the interface region between metallic layers is presented. It is concluded from this study that the extent of the distortion of the interface region due to ion induced broadening is dependent not only on the material system used but on the experimental conditions employed as well. Lastly, radiation enhanced diffusion (RED) has been studied using Ag/Ni thin-film multilayered structures. A physical mathematical model of the radiation broadened Ag layer, capable of successfully deconvoluting the contributions to interface broadening due to RED from those due to cascade mixing and microstructure development, is presented and shown to be an accurate characterization of the interface region. It is concluded from the application of this model that RED can contribute substantially to interface broadening in multicomponent systems with low activation energies of diffusion. It is further concluded from this study that elevated temperatures, sustained during the depth profiling process, can cause the effects of RED to subside dramatically. This phenomenon is most probably due to the dispersion of complex defects responsible for the RED process.Item Measurements of the Size Distribution and Aerodynamic Properties of Soot(1989) Cleary, Thomas George; Gentry, James W.; Chemical and Biomolecular Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)The particle size distribution and aerodynamic properties of soot agglomerates formed by the combustion of acetylene is studied. A positive pressure soot generator was constructed which allowed for the characterization of the soot aerosol. Nearly monodisperse particles (10 to 20 nm in diameter) have been observed at low acetylene flow rates. The mean size and width of the distribution are confirmed with a diffusion battery and a differential mobility analyzer. Size distribution measurements of soot agglomerates have been obtained from optical and electron microscopy for a range of acetylene flow rates. The electron microscopy results are compared to model predictions of the cluster size distribution. Friction coefficient measurements from electrical mobility classified agglomerates have been made and are compared to fractal models for clusters. Aerodynamic diameters of impacted agglomerates are related to the geometric mean size form optical microscopy. These results suggest that the geometric mean size can replace the spherical diameter if a particle density of 0.1 g/cc is assumed.