The aim of this thesis is to investigate the effects of interstellar processing using presolar samples. Dust in the interstellar medium is predicted to have experienced grain-grain and grain-gas collisions, cosmic-ray bombardment, or the formation of ices on their surfaces. Each process is likely to have altered presolar grains. The grains are extracted from meteorites and can be analyzed in the laboratory to try and understand these processes. The main analytical tool used in this research was a new time-of-flight secondary ion mass spectrometry instrument equipped with a Au-cluster primary ion source. Analysis of presolar grains required that a rigorous experimental procedure was developed. A depth-profiling technique for the analysis of micron-sized samples was produced and the limitations of the technique considered. Secondary ion mass spectrometry suffers from matrix effects, so homogeneous silicate glass standards were analyzed. The use of Au-cluster primary ions was shown to enhance practical secondary ion yields relative to those with Au+, consistent with increased sputter rates. Relative sensitivity factors for major and trace elements in the standards were obtained using both normal and delayed secondary ion extraction techniques. Depth-profiles of Li, B, Mg, Al, K, Ca, Ti, V, Cr and Fe were obtained from eleven presolar SiC grains. In some SiC grains, the abundances of several elements were up to orders-of-magnitude higher in the outer ~200nm relative to the grain cores. This was attributed to the implantation of interstellar matter, accelerated to velocities of ~1000kms-1 by supernovae shockwaves. Other SiC grains contained homogeneously distributed trace elements, or evidence of elemental zoning, which could be explained by condensation processes around the grains' parent stars. These grains must have experienced minimal processing in the interstellar medium. It is suggested that the two populations represent SiC grains whose residence times in the interstellar medium significantly differed, consistent with previous findings of noble gas and Li isotopic studies. A further study investigated carbonaceous grains isolated from the Murchison meteorite using a size and density procedure adapted for presolar graphite. No graphite grains were found and possible reasons for this are discussed. The structural and isotopic natures of thirty-three carbonaceous grains were determined by correlated, multi-instrument analyses. The grains contained solar C, N and O isotopic compositions. Deuterium was enriched in the grains with δD values up to +333 ± 110‰. These enrichments suggest exchange of H with cold interstellar gas in the outer part of the early solar nebula or interstellar medium. Raman spectroscopic and transmission electron microscopic analysis showed the grains to be composed of carbon more structurally disordered and amorphous than most carbonaceous phases observed in extra-terrestrial samples. It is argued that amorphization of the grains occurred through solar wind ion irradiation in the proto-solar nebula. This model is supported by previous studies of terrestrial soot and carbon-rich ices irradiated by H⁺ and He⁺ ion doses of ~10¹⁵ - 10¹⁶ ions cm⁻². Implantation and mixing of H⁺ ions is likely to have diluted the grains' original H isotopic composition.

The aim of this thesis is to comprehensively analyse presolar silicon carbide (SiC) grains from several primitive meteorites in order to investigate their complicated history. During their residence in the interstellar medium, presolar grains are predicted to be affected by many processes which may modify their original elemental and isotopic composition. Presolar SiC grains from three acid residues and two polished meteorite sections were analysed for their carbon, nitrogen and silicon isotope ratios with high spatial resolution, in order to compare the distribution of 14N/15N ratios compared to those found in the literature. As a result of this work, isotopic fractionation effects caused by the distortion of the electric field around the grain topography were identified. These effects have the potential to cause differential transmission of atomic and molecular secondary ions, particularly when small slits and apertures are selected during NanoSIMS analyses. The measured 14N/15N ratios of the presolar SiC grains analysed in this work match well with existing literature data, although many grains cluster at relatively low 14N/15N values. These low ratios do not appear to be the result of either terrestrial contamination or isotopic dilution, and may instead represent real differences between the SiC grain populations of different meteorites. The majority of mainstream SiC grains analysed in this work lie on a slope with a gradient of ~1.3 on a Si 3-isotope plot, in agreement with literature data. SiC grains from the JAMM and JA-MM2 acid residues appear to lie on shallower slopes, although these samples show significant scatter in the data. Neither terrestrial contamination nor isotopic dilution can explain the apparent fractionation of silicon isotopes in these samples. It is possible that these ratios may represent a difference in the Si ratios of grain populations of different meteorites, although fractionation during the sample preparation phase cannot be excluded. Ten presolar SiC grains from the KJG and JA-MM2 acid residues are comprehensively analysed for their trace element compositions using Time-of-Flight Secondary Ion Mass Spectrometry. The majority of analyses are significantly affected by the proximity of neighbouring grains, leading to high background counts which prevent the reliable determination of elemental abundances for many elements. Depth profiles of several elements are determined for two grains from the KJG residue. Each of the measured elements displays approximately homogeneous profiles through the grains, with abundances in agreement with existing literature data. The uniform depth profiles may represent formation in a stellar envelope with a stable composition, although homogenisation by secondary alteration processes cannot be ruled out.