Raman modes of the deformed single-wall carbon nanotubes

TL;DR

This study uses empirical and ab initio methods to analyze how uniaxial and torsional strains affect the Raman spectra of single-wall carbon nanotubes, revealing shifts, new peaks, and symmetry effects.

Contribution

It provides a systematic analysis of strain effects on Raman spectra of SWCNTs, including the discovery of new peaks under torsional strain and the linear shift of high-frequency modes.

Findings

High-frequency Raman modes shift linearly with uniaxial strain.

New Raman peaks appear under torsional strain due to symmetry breaking.

Low-frequency modes are largely unaffected by deformation.

Abstract

With the empirical bond polarizability model, the nonresonant Raman spectra of the chiral and achiral single-wall carbon nanotubes (SWCNTs) under uniaxial and torsional strains have been systematically studied by \textit{ab initio} method. It is found that both the frequencies and the intensities of the low-frequency Raman active modes almost do not change in the deformed nanotubes, while their high-frequency part shifts obviously. Especially, the high-frequency part shifts linearly with the uniaxial tensile strain, and two kinds of different shift slopes are found for any kind of SWCNTs. More interestingly, new Raman peaks are found in the nonresonant Raman spectra under torsional strain, which are explained by a) the symmetry breaking and b) the effect of bond rotation and the anisotropy of the polarizability induced by bond stretching.