NESTED POLYHEDRA OF MX(2) (M=W, MO X=S, SE) PROBED BY HIGH-RESOLUTIONELECTRON-MICROSCOPY AND SCANNING-TUNNELING-MICROSCOPY

Extensive investigation of the newly discovered fullerene-like nested polyhedra (NP) and nanotubules of metal dichalcogenides by scanning tu nneling microscopy (STM) and high-resolution transmission electron mic roscopy is reported. Long-term spontaneous (room temperature) and elec tron beam assisted crystallization of amorphous precursor into NP or M X(2) (M = W, Mo; X = S, Se) was observed. This, along with other findi ngs, suggests that the NP constitute a new metastable phase between th e starting amorphous material and the thermodynamically stable bulk 2H allotrope. Characterization of the apex angles by STM suggests that t he apexes of the NP may contain geometrical elements such as triangles and rhombuses, which do not exist in nested carbon fullerenes. The en ergy bandgap of the NP, determined using STM, was found to be somewhat smaller than that of the bulk 2H phase, and possible explanations for that phenomenon are forwarded.