Phonons in MS<inf>2</inf> (M=Mo, W) nanotubes

Abstract

Using full symmetry implemented valence-force-field model, we have calculated phonon energies of all the single-wall MS2 nanotubes with diameter range 1-20 nm. In particular, we extracted infrared and Raman active modes in order to clarify possible application of these methods in the experimental sample characterization. A prescription for experimental distinction of zig-zag, armchair and chiral tubes, based on their different symmetry and resulting selection rules, is proposed. Furthermore, we noticed that displacements significantly depend on the chiral angle only for two MoS2 modes, namely twisting in-phase (rigid layer) and breathing out-of-phase, and none of WS2 modes. Also, we found that heat capacity of the nanotubes and corresponding layer are similar. © 2007 American Institute of Physics.