Synthesis and carbothermal nitridation mechanism of ultra-long single crystal α-Si3N4 nanobelts.

One-dimensional Si3N4 nanostructures are desirable for constructing nanoscale electric and optoelectronic devices due to their peculiar morphologies. Herein, a facile and environmentally friendly catalyst-free method is proposed to synthesize ultra-long single crystal alpha-Si3N4 nanobelts via carbothermal nitridation of carbon nanotubes at 1750 degrees C. The obtained alpha-Si3N4 nanobelts with a flat surface (thickness of similar to 150 nm, length of several millimeters) exhibited an extremely high aspect ratio, perfect crystal structure, and high specific surface area of 7.34-10.09 m(2) g(-1). In addition, the width was increased from approximately 80 nm to 8 mu m by increasing the holding time from 1 to 3 h. The nanobelt formation was governed by the vapor-solid (VS) reaction between SiO vapor, N-2 and carbon nanotubes, and the vapor-vapor reaction between SiO, CO and N-2. The former was responsible for the initial nucleation and successive base-growth of alpha-Si3N4 nanotubes. The latter additionally contributed to the nanorod and subsequent proto-nanobelt formation and to the growth of the nanobelts. During high-temperature annealing at 1750 degrees C, the original Si3N4 nanotubes gradually transformed into nanorods, and, finally, nanobelts with stable shapes as a result of surface energy minimization.