Browsing by Subject "silver"
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Item Heteroepitaxial Self Assembling Noble Metal Nanoparticles in Monocrystalline Silicon(2013-08-13) Martin, Michael S.Embedding metal nanoparticles in crystalline silicon possesses numerous possible applications to fabricate optoelectronic switches, increase efficiency of radiation detectors, decrease the thickness of monocrystalline silicon solar panels and investigate fundamental properties. Noble metal nanoparticles made of gold or silver are grown in cavities in monocrystalline silicon formed by helium ion implantation and high temperature annealing at depth greater than 500 nm from the surface. Metals are introduced into the system by low energy ion implantation or physical vapor deposited thin film on the surface, and diffused into cavities by heat treatment. Nanoparticles nucleate on the inner surface of cavities heteroepitaxially and form face centered cubic crystal structure in the case of silver. Excessive heat treatment causes metal to be emitted from nanoparticles into bulk after trapping and nanoparticle formation. Helium ion implantation, annealing and diffusion heat treatment conditions have been optimized so that residual crystalline damage, point defects and dislocations, is reduced in monocrystalline silicon substrate.Item Synthesis and Properites of Nanotwinned Silver and Aluminum(2013-07-31) Bufford, Daniel CRecent studies of fcc metals with dense twins (~10 nm spacing) have revealed impressive mechanical properties, along with improved ductility and electrical conductivity in comparison to nanocrystalline metals with similar feature sizes. Many important fcc metals could benefit from these ?nanotwinned? microstructures, however, not all fcc metals readily form such twins. The tendency of fcc metals to form twin boundaries is related to the twin boundary energy; those with low twin boundary energy, such as silver (Ag), easily form twins. Increasing twin boundary energy interferes with twin formation, to the point that in metals with high twin boundary energy, like aluminum (Al), twins are quite rare. This thesis focuses on the synthesis of nanotwinned Ag and Al via physical vapor deposition. Nanotwinned Ag is readily fabricated, however, a template approach had to be developed to induce twins in Al. The microstructures and their relationships to observed mechanical properties are also discussed. Grain boundaries interfere with dislocation transmission by posing a slip system discontinuity between grains. Twin boundaries are a special class of grain boundaries in which the grains on either side of the boundary are related by mirror symmetry. Twin boundaries inhibit dislocation transmission, providing strength in the same manner as grain boundaries. However, their symmetrical structure reduces the free volume and grain boundary energy. Accordingly, coherent twin boundaries are often more energetically stable than grain boundaries, and their coherency allows plasticity mechanisms to remain active under conditions where such mechanisms may be inhibited at grain boundaries. Hence, twin boundaries may provide a metal with unique combinations of high strength and good ductility, conductivity, and thermal stability.Item The Role of Neutron Activation Analysis in the Pathological Evaluation of Silver-Eluting Biomedical Devices in Biological Matrices(2014-08-14) Lancon, TrevorThe purpose of this research was to determine the viability of using instrumental neutron activation analysis (INAA) to quantify silver nanoparticle (AgNP) content in biological matrices in the context of pathology evaluations of silver-eluting devices for United States Food and Drug Administration (FDA) approval. This work was comprised of feasibility, experimental, and simulation stages. The extent of how AgNPs presented through transmission electron microscopy (TEM), scanning electron microscopy (SEM) with energy-dispersive X-ray microanalysis (EDX), and INAA methodologies within porcine skin was explored in the feasibility trial. Sections of skin containing control and test articles were investigated using these modalities. The control article was skin that contained a driveline coated in material known to elute AgNPs into tissue. TEM findings supported the conclusion that the host reacted to the presence of larger AgNP aggregates surrounding the control article at an ultrastructural level. The test article was skin that contained a driveline coated in material hypothesized to not elute AgNPs into surrounding tissue. AgNPs were not observed to aggregate throughout the tissue adjacent to the test article, and a marked host reaction to their presence was not observed. INAA results correlated with these findings; silver was not detected adjacent to the test article, but a concentration of 74 ppm ? 29% of silver was observed in tissue adjacent to the control article. A complex system of ordinary differential equations (ODEs) was constructed to determine the inventory of the activation and subsequent decay progeny produced in a sample containing silver exposed to a neutron field. These ODEs were constructed into a Simulink? model and benchmarked using experimental data. This system was simplified after showing that production of induced ^(109)Ag during irradiation of silver did not significantly affect elemental silver estimation by measurement of ^(110m)Ag. Results from this model suggested that samples should be irradiated for up to 120 s and allowed to decay for 7 d before gamma ray spectroscopy is performed when investigating silver content in similar sodium-rich biological matrices via INAA in the future.