Growth mechanism of Si3N4nanowires from amorphous Si3N4powders synthesized by low-temperature vapor-phase reaction

A novel synthesis method to prepare Si3N4 nanowires from amorphous silicon nitride (a-Si3N4) powder synthesized by a low-temperature vapor-phase reaction method was investigated. Highly crystalline α-Si3N4 nanowires were synthesized by heat treatment of the a-Si3N4 powder under ammonia atmosphere. The surface of the nanowires was smooth and clean without any attached particles. The thickness of the nanowires was in the range of ∼200–300 nm with lengths of tens of micrometers. The nucleation of nanowires from the reaction between SiO and N2 occurs on the surface of the a-Si3N4 powder, which is covered by a thin layer of SiO2, and the nanowires grow from the rearrangement of Si and N atoms of the a-Si3N4 powder. The reduction of SiO2 to SiO by ammonia was promoted in the presence of a Ni catalyst; therefore, the growth was observed at a lower temperature when Ni was added to the a-Si3N4 powder than in the presence of added Fe. The growth of α-Si3N4 nanowires occurs along the [100, 101] direction and follows the vapor–solid–solid mechanism.