Size and shape dependent Raman scattering of WS₂ nanomaterials

Fullerene-like WS₂ nanoparticles and WS₂ nanotubes are studied by wavelength dependent Raman spectroscopy. The response from the nanomaterials is compared to that of 2H-WS₂ crystals and microcrystalline 2H-WS₂ powder. The Raman signatures point to a hexagonal 2H stacking of the WS₂ layers in all nanostructures. While the wave numbers of 1^st and 2^nd order Raman scattering show only little dependence, the line widths and the intensity ratios exhibit a systematic evolution with respect to the specific WS₂ nanostructure. The sulfur-sulfur stretching mode range is particularly sensitive to the different stages of disorder and is suitable for the diagnostic classification of the WS₂ nanostructures. Raman mapping across the nanoparticles is used to distinguish between disorder and surface effects on the vibrational spectra. All the experiments were performed at low laser power, since the transformation into WO₃ is induced already at moderate illumination due to the limited photo- and thermal stability of the materials.

This work is supported by the European Union sixth Framework Program (FOREMOST project under contract NMP3-CT-2005-515840).