Structural properties of MoS₂ “mama”- tubes and related materials

MoS₂ nanomaterials synthesized by sulphurization of Mo₆S₂I₈ nanowires were studied by wavelength dependent Raman spectroscopy, X-ray diffraction, and high resolution transmission electron microscopy (HRTEM). The transformation process leads to a variety of selective morphologies of the MoS₂ product, like coaxial nanotubes, i.e. nanotubes with split walls, “mama”- tubes with encapsulated MoS₂ fullerene-like particles, or other hybrid nanostructures. The temperature inside our horizontal fluidized-bed reactor directly determines the final morphology of the product. A temperature above 850°C leads to a formation of MoS₂ “mama”– tubes, while below 850°C the growth of coaxial MoS₂ nanotubes in which a number of multiwall nanotubes grow coaxially separated by gaps is favored. HRTEM was used to study how MoS₂ layers form from outside of precursor nanowires toward inside and to observe the nucleation of fullerene-like particles. Results of a possible oxidation during the Raman experiments are correlated with partially or fully oxidized Mo₆S₂I₈ nanowires of the composition MoO_3-x, which can be afterwards also sulphurized resulting in MoS₂ polycrystalline nanowires.
By the means of Raman and X-ray diffraction spectroscopies we have studied effect of temperature and duration of the sulphurization process. We followed the stages of the transformation to explore the chemical reaction kinetics.