Meteoritic Nanodiamond Carbon Isotope Analysis
Microscopy Method Goes Deep, Atom-probe tomography reveals the 3-D positions of atoms inside hard-to-analyze materials, Mitch Jacoby, Chemical and Engineering News, Cover Story, Volume 92, Issue 41, pp. 11-14 (13 October 2014)
Philipp R. Heck, an assistant curator at Chicago’s Field Museum, together with a team of researchers from about 10 institutions, applied similar methods to determine the carbon-12 to carbon-13 ratio in meteoritic nanodiamonds. Samples, which the team embedded in platinum tips, came from the thoroughly studied Allende meteorite, a massive rock that predates the solar system and broke up over northern Mexico in 1969.
The team’s aim was to determine whether carbon’s isotope distribution in the nanodiamonds differs markedly from its distribution on Earth. Finding such a sample would suggest that the carbon was formed via a nucleosynthesis method different from the one that formed Earth’s carbon. Major differences in isotope abundances have been measured in other extraterrestrial material. So far, the nanodiamond study has not turned up obvious differences in carbon isotope distributions.
But it’s not “case closed” just yet. The analysis has proved difficult because it pushes APT’s detection limits. The nanodiamond study requires accurately counting and sorting very small numbers of atoms from approximately 3-nm-diameter particles and spotting a difference from the earthly 13C abundance, which is only 1.1%. The investigation has so far shown that APT is well suited to the cosmic science task, but larger data sets need to be generated.
Meteorit. Planet. Sci. 2014, DOI: 10.1111/maps.12265
Atom-probe analyses of nanodiamonds from Allende, Philipp R. Heck, Frank J. Stadermann, Dieter Isheim, Orlando Auciello, Tyrone L. Daulton, Andrew M. Davis, Jeffrey W. Elam, Christine Floss, Jon Hiller, David J. Larson, Josiah B. Lewis, Anil Mane, Michael J. Pellin, Michael R. Savina, David N. Seidman and Thomas Stephan. Meteoritics & Planetary Science, Volume 49, Issue 3, pages 453–467 (4 March 2014)
Atom-probe tomography (APT) is currently the only analytical technique that, due to its spatial resolution and detection efficiency, has the potential to measure the carbon isotope ratios of individual nanodiamonds. We describe three different sample preparation protocols that we developed for the APT analysis of meteoritic nanodiamonds at sub-nm resolution and present carbon isotope peak ratios of meteoritic and synthetic nanodiamonds. The results demonstrate an instrumental bias associated with APT that needs to be quantified and corrected to obtain accurate isotope ratios. After this correction is applied, this technique should allow determination of the distribution of 12C/13C ratios in individual diamond grains, solving the decades-old question of the origin of meteoritic nanodiamonds: what fraction, if any, formed in the solar system and in presolar environments? Furthermore, APT could help us identify the stellar sources of any presolar nanodiamonds that are detected.
Meteoritic Nanodiamond Analysis by Atom-Probe Tomography, J. B. Lewis, D. Isheim, C. Floss, T. Daulton, D. N. Seidman, P. R. Heck, A. M. Davis, M. J. Pellin, M. R. Savina, J. Hiller, A. Mane, J. Elam, O. Auciello, T. Stephan, Microsc. Microanal. 20 (Suppl 3), 2014
New Atom-Probe Tomography Data and Improved Techniques for Meteoritic Nandiamond Analysis, J. B. Lewis, D. Isheim, C. Floss, T. L. Daulton, D. N. Seidman, 45th Lunar and Planetary Science Conference (2014)
These are the carbon isotope analyses that have not yet been done, and remain to be applied to the so called sedimentary nanodiamonds from the Younger Dryas boundary horizon sediments.