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Meteoritic Nanodiamonds


Figure 5 : Ion fraction detected in the atom-probe as a function of C isotopic ratio for four sets of ions: N, O, PtOC+Na+NaO, and C+(2×C 2 )+(3×C 3 ). The left graph is plotted against a ratio of C isotopes with a charge of 2+, and the right graph is plotted against a ratio of C isotopes with 1+ charge. None of the sets show any linear trend, except for O and C ions for the ratio of 1 + charge state C isotopes, which do exhibit weak linear trends. These two trends may suggest that contaminant-rich material in the acid residue, (disordered C) and material rich in uncontaminated C (nanodiamonds) form from two different stellar sources with different C isotopic ratios. However, these data may be exhibiting hydride interference (see text).


of acid residue that are dominated either by nanodiamonds or disordered carbon. T is analysis is based on previous fi ndings that nitrogen is more likely to form in nanodiamonds. An initial comparison with the 12 C/ 13 C ratios of the microtips suggests that disordered, probably glassy carbon, has similar 12 C/ 13 C ratios to the nanodiamonds, indicating they may have formed from the same isotopic reservoir. Small diff erences between the isotopes in the two phases appear to be indicative of hydride formation proceeding more readily on disordered C than on nanodiamonds.


We expect that complementary or correlated studies by transmission electron microscopy, while potentially more conclusive in its identifi cation of phases, may not always be necessary to distinguish between diff erent material phases in the APT. Contaminant ions, which are more likely to form in each phase, may be used to distinguish phases.


Acknowledgments


This work is supported by NASA grants NNX14AP15H (J.B.L.) and NNX16AD26G (C.F.). The Cameca LEAP atom probe tomograph at the Northwestern University Center for Atom Probe Tomography (NUCAPT) was acquired and upgraded with NSF DMR-0420532 and ONR-DURIP N00014-0400798, N00014-0610539, N00014- 0910781 equipment grants. NUCAPT received support from the MRSEC program (NSF DMR-1121262) at the Materials Research Center, the SHyNE Resource (NSF NNCI-1542205), and the Initiative for Sustainability and Energy at Northwestern (ISEN)).


References [1] RS Lewis et al ., Nature 326 ( 1987 ) 160 – 62 . [2] TJ Bernatowicz et al ., Astrophys J 359 ( 1990 ) 246 – 55 . [3] RM Stroud et al ., Astrophys J Lett 738 ( 2011 ) L27 – L31 . [4] E Zinner , Presolar Grains . in Treatise on Geochemistry 2nd Ed. ( Vol. 1 ), eds. H Holland and K Turekian, Elsevier , Oxford, UK , 2014 .


[5] SS Russell et al ., Met and Planet Sci 31 ( 1996 ) 343 – 55 . 22


[6] TL Daulton et al ., Geochim et Cosmochim Acta 60 ( 1996 ) 4853 – 72 .


[7] PR Heck et al ., Met and Planet Sci 49 ( 2014 ) 453 – 67 . [8] D Isheim et al ., Microsc Microanal 19 ( Suppl 2 ) ( 2013 ) 974 – 75 .


[9] JB Lewis et al ., Ultramicroscopy 159 ( 2015 ) 248 – 54 . [10] NR Greiner et al ., Nature 333 ( 1988 ) 440 – 42 .


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