Raman scattering of the MoS2 and WS2 single nanotubes

We report here the results of the first resonance Raman study on single MoS₂ and WS₂ nanotubes and microtubes synthesized by chemical transport reaction. These multiwall tubes represent the longest known inorganic nanotubes grown up to several millimetre lengths with diameters ranging from less than ten nanometers to several micrometers. The nanotubes grown at nearly equilibrium conditions contain extremely low density of structural defects. The selected area diffraction on the thick-wall nanotubes revealing the rhombohedral (3R) stacking, otherwise stable at elevated pressure above 4 GPa, provides indirect evidence of the presence of strain incorporated into the nanotube wall. Results are compared with phonon spectra of plate-like crystals of the same compound. The observed up-shift of Raman peaks in the tubes spectra is explained by the presence of strain. Well preserved crystal structure of tubes is confirmed by comparison with phonon spectra of nanostructured materials from literature.