Structure and Stability of Molybdenum Sulfide Fullerenes

MoS2 nanooctahedra are the smallest stable close-cage structures of MoS2, i.e. the genuine inorganic fullerenes. Here, a combination of experiments and density-functional tight-binding calculations with molecular dynamics annealing are used to elucidate the structures and electronic properties of octahedral MoS2 fullerenes. The calculations show that the octahedra are stable beyond n(Mo)>100, but with the loss of 12 S atoms at the six corners. In contrast to the semi-conducting bulk and nanotubular structures, the Fermi level of the octahedra is situated within a band, hence the nano-octahedra are metalloid. A model derived from these calculations for the treatment of larger structures shows that, in agreement with experiment, multiwall nanooctahedra are stable over a limited size range of about 10^4 to 10^5 atoms; beyond that size, the clusters are converted into spherical nanoparticles. These theoretical findings concerning the critical size for the structural transition, the under-stoichiometry in S, and the electronic nature of the nanooctahedra are confirmed by TEM experiments on particles synthesized by laser ablation.