Formation of small single-layer and nested BN cages under electron irradiation of nanotubes and bulk material

An experimental evidence for the formation of small BN cage-like molecules, under electron-irradiation experiments of BN samples, is presented. Depending on the starting material, either close-packed agglomerates of small "fullerenes", or small nested "fullerenes" with up to six layers are found as irradiation derivatives. The overall polyhedral shape of the BN cages is explained within the frame of the octahedral model previously proposed for BN analogs to fullerenes. The diameters of the smallest and most observed cages range from 0.4 to 0.7 nm, and are close to those of the B₁₂N₁₂, B₁₆N₁₆ and B₂₈N₂₈ octahedra which were predicted to be magic clusters for the BN system from electronic structure calculations.