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Abstract

Presolar, circumstellar silicates have been positively identified by their highly anomalous oxygen isotopic compositions using secondary ion mass spectrometry (SIMS), yet presolar, interstellar silicates have eluded unambiguous discovery. Glass with embedded metal and sulfides (GEMS)—amorphous silicates that are an abundant constituent of primitive interplanetary dust particles (IDPs)—have been proposed to be these interstellar grains. Circumstellar silicates and GEMS may therefore represent related and consecutive stages in the lifetime of cosmic silicates. A competing hypothesis is that GEMS are vapor-phase, nonequilibrium condensates from the early solar nebula. In either case, GEMS may also be precursors to the amorphous silicates in primitive meteorites prior to parent body processing. The various silicate components of different primitive samples may represent various related stages in silicate dust evolution—from condensation around stars, interstellar medium processing, incorporation into growing planetesimals in protoplanetary disks, to subsequent parent body processing. Analytical challenges have impeded the nanometer-scale components of fine-grained, extraterrestrial materials from being fully characterized. This dissertation explores techniques in sample preparation and quantitative microanalysis to allow for detailed characterizations of these components at an unprecedented level of accuracy and precision. Applying new methods of sample preparation using focused ion beam (FIB) milling in combination with scanning transmission electron microscopy (STEM) nanodiffraction and resonance ionization mass spectrometry (RIMS), we demonstrate how seemingly morphologically and chemically similar materials at the micrometer scale can show significant differences at the nanometer scale and sheds light on the ancestral connections, or lack thereof, between these enigmatic types of grains.

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