Local Structure and Bonding of Carbon Nanothreads Probed by High- Resolution Transmission Electron Microscopy

SJ Juhl and T Wang and B Vermilyea and X Li and VH Crespi and JV Badding and N Alem, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 141, 6937-6945 (2019).

DOI: 10.1021/jacs.8b13405

Carbon nanothreads are a new one-dimensional sp(3)-bonded nanomaterial of CH stoichiometry synthesized from benzene at high pressure and room temperature by slow solid-state polymerization. The resulting threads assume crystalline packing hundreds of micrometers across. We show high- resolution electron microscopy (HREM) images of hexagonal arrays of well-aligned thread columns that traverse the 80-100 nm thickness of the prepared sample. Diffuse scattering in electron diffraction reveals that nanothreads are packed with axial and/or azimuthal disregistry between them. Layer lines in diffraction from annealed nanothreads provide the first evidence of translational order along their length, indicating that this solid-state reaction proceeds with some regularity. HREM also reveals bends and defects in nanothread crystals that can contribute to the broadening of their diffraction spots, and electron energy-loss spectroscopy confirms them to be primarily sp a -hybridized, with less than 27% sp(2) carbon, most likely associated with partially saturated "degree-4" threads.

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