Co-produced carbon and boron nitride helical cones and the nucleation of curved BN sheets

Abstract

Abstract The structure of carbon (C) and boron nitride (BN) columnar particles produced alongside by heat-treating a turbostratic B—C—N compound was investigated by analytical transmission electron microscopy. The particles were shown to be helical cones with a well-defined apex, and a helical pitch equal to usually one and at most two layers. The cone apex angle distribution was found to be centred on different values for C and BN. These results strongly suggested that BN and C cones nucleated from different ring defects in the hexagonal networks: square-like ring defects in BN and pentagon-like ring defects in C. These observations were consistent with the supposition that the creation of non B—N bonds and hence odd-membered rings is avoided in BN. Such restriction in BN could also allow one to understand the observed morphological differences between C and BN cones, and in particular the relative difficulty for BN cone edges to join via curved sheets.