Raman Spectroscopy of Individual Suspended Carbon Nanotubes under Immense Strains

Suspended carbon nanotubes with long nanotube-substrate contacts grown by chemical vapor deposition enable us to explore carbon nanotubes up to strains of 13.6{\%}. Here, Raman spectroscopy is utilized to observe strain-induced changes in the $G$ band vibrational modes, which have a linear and pronounced response to the extension of the C-C bonds under various degrees of strain. The $G$ band is found to downshift at rates ranging from -6.2 to -23.6cm$^{-1}$/{\%} strain among the different nanotubes measured in this study. Despite this wide range of downshift coefficient, we observe broadening of the $G$ band linewidth (FWHM) at a universal threshold downshift of $\Delta \omega _{G }>$ 75cm$^{-1}$. The $G$ band is observed to downshift by up to 157cm$^{-1}$ (from 1592 to 1435cm$^{-1})$ under immense strains without any noticeable $D$ band. Our measurements show that carbon nanotubes remain intact up to 13.6{\%} strain with no slippage, breakage, or defect formation.