Environmental effects, intertube interactions and σ-π bond re-hybridization in bundles of double- and triple-walled carbon nanotubes.

In the literature, fine structuring and mixing of the radial breathing mode frequencies ( ω RBM ) due to intertube interactions ( Ω int ) for specific inner tubes in free-standing isolated double-walled nanotubes (DWNTs) have been addressed. Questions and arguments related to the Ω int nature and its dependence with the nanotube's growth processes have also been addressed. Later, studies involving bundled (innermost tubes) and isolated (innermost and middle tubes) of triple-walled nanotubes (TWNTs) for diameters between 0.5 and 1.7 nm found no ω RBM fine structuring or mixing but suggested that the Ω int depends on the tube's metallicity. Here, Raman Spectroscopy is combined with transmission electron microscopy (TEM) to show that for bundled DWNTs and TWNTs measured in a broad diameter range (0.5 ≤ d t ≤ 2.8 nm) three effects seem to be fundamental to explain the ω RBM behavior of their constituent tubes: interactions with the external environment, metallicity-independent Ω int and curvature effects due to σ-π bonds re-hybridization. Our results display no evidence of ω RBM mixing but show that Ω int has no apparent dependence with the growth process and that Ω int has the same nature of the tube interactions with the environment. The manuscript also discusses the thus far elusive TWNT outermost tubes ω RBM . Image 1 [ABSTRACT FROM AUTHOR]