Stable BC2N nanostructures:: low-temperature production of segregated C/BN layered materials

Stable filaments of nanometer dimensions with overall chemical stoichiometry close to BC2N were generated by pyrolysis of CH3CN . BCI3 over Co at 1000 degrees C and, for the first time, their structures were investigated, at the nanometer level, using high spatial resolution electron energy-loss spectroscopy. Concentration profiles, along and across the filaments, revealed that B, C and N are not homogeneously distributed within the nanostructures but are separated into pure C and BN domains. Interestingly, pure h-BN layers are always sandwiched between graphite-like shells. A two-stage growth process is proposed involving: (a) initial extrusion of a pure carbon filament from the catalytic particle, followed by (b) subsequent thickening of the BN and C layers precipitated from the gas phase. This pyrolytic technique provides an alternative and efficient route to segregated BN/C nanomaterials, which may prove useful as robust nanocomposites and semiconductor nanodevices with enhanced resistance towards oxidation. (C) 1999 Elsevier Science B.V. All rights reserved.