RBM frequencies of the SWCNTs as a function of aspect ratio. The SWCNTs have the same axial half-wave numbers, m = 1, and axial pressures, px = 1 TPa. However, they have circumference wave numbers n that vary from 1 to 4.
Lei et al. Nanoscale Research Letters 2011 6:492 doi:10.1186/1556-276X-6-492