Novel coaxial SiC-SiO₂-BN nanocable: Large-scale synthesis, formation mechanism and photoluminescence property

Novel one-dimensional heterostructures composed of single crystalline cubic SiC cores, intermediate amorphous SiO₂ layers, and single crystalline hexagonal BN (h-BN) sheaths (i.e. SiC-SiO₂-BN nanocable) have been successfully fabricated in large scale using SiC-SiO₂ nanocables and ammonia borane as starting materials. The structure and chemical composition of the as-synthesized products are determined by powder X-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and energy filtered TEM based on electron energy loss spectroscopy. The nanocables are approximately 100 nm in diameter and up to 1 millimetre in length. The intermediate amorphous SiO₂ layers and the outer h-BN sheaths are about 10 nm and 5 nm thick, respectively. Interestingly, an increase in the amount of ammonia borane leads to the transformation of SiC-SiO₂ nanocables into BN nanotubes. Mass spectrometric analysis shows that the vapors decomposed from ammonia borane play crucial roles both in the growth of the BN sheath on the SiC-SiO₂ nanocables and in the transformation to the BN nanotubes. The SiC-SiO₂-BN nanocable displays similar photoluminescence (PL) characteristics with respect to the original SiC-SiO₂ nanocable but with the 488.5-nm emission peak blue shifting. The synthetic route has also been extended to fabricate SiC-BN nanocables and has proved effective and universal for the synthesis of core-sheath nanostructures with BN sheaths.