Sound wave propagation in multiwall carbon nanotubes

Abstract

This article studies transverse sound wave propagation in individual multiwall carbon nanotubes. The present model predicts that there exist (N-1) critical frequencies (within terahertz range) for an N-wall carbon nanotube. When the frequency is below all critical frequencies, vibrational mode is almost coaxial and the associated sound speed can be predicted satisfactorily by the existing single-elastic beam model. However, when the frequency is higher than at least one of the critical frequencies, non-coaxial vibrational modes emerge which propagate at various speeds significantly higher or lower than the speed predicted by the single-elastic beam model. Hence, terahertz sound waves in multiwall carbon nanotubes exhibit complex phenomena and are essentially noncoaxial. In particular, terahertz sound waves in multiwall carbon nanotubes propagate at various speeds, depending not only on the frequency but also on the noncoaxial vibrational modes.