Graduate Citings: Josiah Lewis

Josiah Lewis

6th Year Doctoral Student

12C/13C ratio determination in nanodiamonds by atom-probe tomography

Volume 159, 248-254
Published: June 6, 2015

Three decades ago, researchers identified curious nanoparticles in meteorites. Each containing just a few thousand carbon atoms, these nanodiamonds are the right size to be a wedding ring for an e-coli bacterium. One in a million nanodiamonds contains an atom of xenon, and the ratio of the different isotopes of xenon were unlike anything seen in our solar system. In fact, the isotopic anomalies only match those produced by supernovae explosions. Researchers surmised that some of the nanodiamonds formed in the aftermath of these explosions. But the only way to know for sure would be to measure the ratio of the stable carbon isotopes, 12C and 13C, of individual nanodiamonds.

Only in the past decade has a technique been developed to accomplish this experimental task. Atom-probe tomography uses high voltage and pulses of laser energy to rip one atom at a time from a microscopic, needle-shaped sample. A detector allows us to reconstruct the original position of each atom, and mass spectrometry tells the difference between isotopes of C.

We conducted a suite of atom-probe measurements, and corrected them for a variety of contaminants, instrumental artifacts, and statistical effects that affect our isotopic measurements. Measurements of individual, and small numbers of nanodiamonds, the first of their kind, have yet to reveal significant isotopic anomalies, suggesting that the vast majority of the nanodiamonds may have formed in the early solar system with normal isotopic ratios.

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