Simultaneous in situ and ex situ growth of ultra-long Si3N4 nanobelts with different optical properties

In situ and ex situ growth of ultra-long Si3N4 nanobelts (NBs) was simultaneously achieved via an effective method with the raw materials of graphite, nanosilicon and nanosilica. In situ growth of ultra-long Si3N4 NBs on the surface of the powder mixture resulted in a cross-section of 30-50 nm in thickness and 100-250 nm in width, and a length that can grow up to several millimeters. The width and thickness of the NBs obtained on the inner walls of the crucible, namely ex situ growth of Si3N4 NBs, are in the range of 200-500 nm and 50-200 nm, respectively. A vapor-solid (VS) mechanism was proposed for the growth mode of the in situ growth of Si3N4 NBs, while VS and vapor-liquid-solid (VLS) mechanisms simultaneously existed in the growth of the Si3N4 NBs obtained on the inner walls of the crucible. This method provides an effective way of preparing Si3N4 NBs on an industrial scale. The room-temperature photoluminescence (PL) spectra show that the synthesized alpha-Si3N4 NBs both had two strong emissions peaks, but the PL spectrum of the ex situ NBs shows an obvious red-shift compared to that of the in situ NBs, making it a potential material for applications in special optoelectronic nanodevices.