Raman-modes of index-identified free-standing single-walled carbon nanotubes

TL;DR

This study combines electron diffraction and Raman spectroscopy to identify the structure of free-standing single-walled carbon nanotubes and examines how their vibrational modes relate to their diameter, revealing deviations from existing models.

Contribution

It provides direct structural indices for individual nanotubes and analyzes their Raman modes, challenging the universality of the radial breathing mode diameter relation.

Findings

Confirmed radial breathing mode frequency versus diameter for small tubes

Observed deviations from the inverse diameter relation at larger diameters

Suggested environmental factors or model limitations affect the frequency-diameter relation

Abstract

Using electron diffraction on free-standing single-walled carbon nanotubes we have determined the structural indices (n,m) of tubes in the diameter range from 1.4 to 3nm. On the same free-standing tubes we have recorded Raman spectra of the tangential modes and the radial breathing mode. For the smaller diameters (1.4-1.7nm) these measurements confirm previously established radial breathing mode frequency versus diameter relations, and would be consistent with the theoretically predicted proportionality to the inverse diameter. However, for extending the relation to larger diameters, either a yet unexplained environmental constant has to be assumed, or the linear relation has to be abandoned.