Nanoseashells and nanooctahedra of MoS₂: Routes to inorganic fullerenes

Nanooctahedra of MoS₂ are considered to be the true inorganic fullerenes, exhibiting different properties from the bulk and also other closed-cage morphologies of the same material. These structures are produced in high energy systems where the synthesis is performed far from equilibrium conditions, and the reaction mechanism involved remains unknown. Here, the discovery of two imperfect structures of nanooctahedra - the distorted octahedra and seashell structures with meander-like cross sections - is reported and studied in detail using transmission electron microscopy and quantum-mechanical methods. These nanoparticles can serve to understand the synthesis route by establishing the basic principles of their morphology and stability. The fundamental properties of the inorganic lattice are the basis for matching the projections observed in microscopy images with a suggested atomistic model. Quantum-mechanical calculations are used to estimate their stability and electronic properties. It was concluded that the production of nanooctahedra involves a high temperature stage, where lattice defects enable the formation of a closed structure without a templating particle. Thereafter at lower temperatures, the mixture of products is carried forward and the annealing contributes to the enrichment of the product with more symmetric structures.