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Polygonization and Anomalous Graphene Interlayer Spacing of Multi-Walled Carbon Nanofibers...

by Mina Yoon, Jane Y Howe, Gyula Eres, Zhenyu Zhang
Publication Type
Journal
Journal Name
Physical Review B
Publication Date
Page Number
165402
Volume
75
Issue
16

The graphene interlayer spacing in pure graphite is known to have a minimum value of dmin = 0.3354 nm, while defective graphites typically have larger interlayer spacings. Using transmission electron microscopy and X-ray diffraction, we find that the graphene interlayer spacing in multi-walled carbon nanofibers heat treated above ≈ 2800 K is distinctly smaller than dmin. To explain this unusual observation, we investigate the structural properties of carbon nanotubes using a multiscale approach rooted in extensive first-principles calculations, specifically allowing the nanotube cross-sections to polygonize. We show that, whereas normal nanotubes are favored energetically at low temperatures, the configuration entropy associated with Stone-Wales defect creation at high temperatures makes the polygonal shape of large
nanotubes or nanofibers thermodynamically stable, accompanied by a reduction in the graphene interlayer spacing. These unique predictions are confirmed in further experimental tests.