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Auger spectroscopy has not found widespread application in the geological sciences, largely because specimens are often non-conductors that charge under electron beams. However, it has proven to be useful for the characterization of sub-micrometer mineral grains in certain meteorites, where sample charging issues can be mitigated. We describe the development of analytical protocols for the measurement of presolar silicate grains using Auger spectroscopy and review how this technique has helped our understanding of the stellar origin and subsequent evolution of these grains.
We have analyzed atom probe tomography reconstructions of disaggregated meteoritic material containing nanodiamonds and disordered carbon to determine whether these phases formed in the solar system or whether they predate the solar system and were formed in supernovae or the interstellar medium. We developed a method to distinguish between these two carbonaceous phases in < 100 nm diameter aggregates using the ratios of various native and contaminant molecular species. We find variations in measured 12C/13C ratios between the two phases that suggest hydrides form more readily during field evaporation of the disordered C than the nanodiamonds.
We present a specimen preparation procedure for atom-probe tomography using SemGlu from Kleindiek Nanotechnik, an adhesive that hardens under electron beam irradiation. The SemGlu adhesive is used in place of focused-ion-beam-induced deposition of organo-metallic Pt, W, or C to form a bond between the sample and the substrate during the specimen preparation procedure. We demonstrate the utility of this adhesive-based specimen preparation technique with a correlated atom-probe tomography-scanning transmission electron microscopy study of the iron-nickel alloy kamacite (ferrite, ɑ-iron) in the Bristol iron meteorite and two steel specimens.
Cryogenic transmission electron microscopy (cryo-TEM) has become a powerful tool for probing the structures of soft-matter materials at nanometer or sub-nanometer scale. For many complex molecular fluids (CMFs), the limiting factor in such studies is the preparation of a cryo-TEM specimen that represents the native structure. Plunge freezing of electron-transparent thin films has been widely used, but it is often influenced or even dominated by surface effects and mechanical disturbances of the CMF. In this article, we use liquid crystals as model CMF systems and present the general procedures and typical results of cryo-ultramicrotomy of rapidly frozen “bulk” samples.
Linear image transfer down to a few tens of pm can be attained by a modern Cs-corrected transmission electron microscope. However, it is difficult to accurately evaluate such a high-performance microscope. We examine three-dimensional (3D) Fourier transform (FT) analysis in comparison with diffractogram (2D FT) analysis to evaluate aberration-corrected electron microscopes. The 3D FT can analyze information transfer on the Ewald sphere up to high-angles using a thick sample or a sample containing strong scattering elements. Therefore, the 3D FT analysis is necessary to evaluate Cs-corrected microscopes, especially those equipped with a Cc-corrector, or a monochromator, or microscopes operated at lower voltages.