Manifestation of anharmonicities in terms of phonon modes' energy and lifetime in multiwall carbon nanotubes

The temperature dependent Raman spectromicroscopic study has been carried out to investigate anharmonic effects in multiwall carbon nanotubes (MWCNT). The micro-Raman scattering experiments have been carried out over a wide temperature range of 173-723 K to analyze manifestation of various MWCNT Raman modes' energy and lifetimes. The experimental results indicated non-linear shifts in the peak position of Raman D- and G-bands with temperature. Phonon softening of Raman modes was observed over a wide temperature range from 273-648 K, and hardening of Raman modes was noticed in both, high- and low-, temperature regimes. Temperature dependent shift of the G-peak has been explained on the basis of anharmonic properties of graphite lattice. Contributions from true-anharmonic and quasi-harmonic parts in shifting the G-peak position have also been explained. Interestingly, the variation of peak width for G-peak of MWCNT appeared to be nearly independent of temperature, likely due to the competing effects from the electron-phonon coupling and anharmonic contributions in the observed temperature range. (C) 2020 Elsevier Ltd. All rights reserved.