Intense Raman D Band without Disorder in Flattened Carbon Nanotubes
Emmanuel Picheau, Anthony Impellizzeri, Dmitry V. Rybkovskiy, Maxime Bayle, Jean‐Yves Mevellec, Ferdinand Hof, Hassan Saadaoui, Laure Noé, Abraao Cefas Torres Dias, Jean‐Luc Duvail, Marc Monthioux, Bernard Humbert, Pascal Puech, Chris Ewels, Alain Pénicaud
Abstract
Above a critical diameter, single- or few-walled carbon nanotubes spontaneously collapse as flattened carbon nanotubes. Raman spectra of isolated flattened and cylindrical carbon nanotubes have been recorded. The collapse provokes an intense and narrow D band, despite the absence of any lattice disorder. The curvature change near the edge cavities activates a D band, despite framework continuity. Theoretical calculations based on Placzek approximation fully corroborate this experimental finding. Usually used as a tool to quantify defect density in graphenic structures, the D band cannot be used as such in the presence of a graphene fold. This conclusion should serve as a basis to revisit materials comprising structural distortion where poor carbon organization was concluded on a Raman basis. Our finding also emphasizes the different visions of a defect between chemists and physicists, a possible source of confusion for researchers working in nanotechnologies.