Analogs for Unlayered-Graphene Droplet-Formation in Stellar Atmospheres

Micron-sized presolar carbon-spheres condensed before the origin of our solar system, in the atmosphere of asymptotic-giant-branch stars from carbon atoms dredged up following nucleosynthesis in the stellar interior, have been extracted by dissolution from primitive carbonaceous chondrite meteorites, identified by noble-gas and major-element isotopic analysis, and available to electron microscopists on earth for over two decades [1-4]. Some of these spheres appear to consist of graphite condensed on carbide grains, but others instead show “graphite-onion” rims that surround a spherical-core of unlayeredgraphene i.e. carbon that in diffraction shows graphite (hk0) spacings only. The high spatial-frequency tail of these graphene lines [5] suggests a graphene-sheet coherence-width in the 4-nm size range [1], consistent with electron-phase-contrast images of single (sometimes segmented) edge-on sheets [2,4].