Synthesis and optical property of ultra-long alpha-Si3N4 nanowires under superatmospheric pressure conditions

Large-scale ultra-long (even up to several centimeters) alpha-Si3N4 nanowires have been prepared using N-2 as the nitrogen source, SiO or a mixture of Si and SiO2 as the silicon source, N-2 and Ar as the barrier gas, and CH4 as the reducing gas by a simple catalyst-free CVD route under superatmospheric pressure conditions. The nanowires grown on ceramic boat or corundum substrates, with lengths of several millimeters, even up to several centimeters, and average diameters of around 40nm, were composed of a single-crystal alpha-Si3N4 core along the [210] direction and amorphous SiO2 shell of about 1-10 nm thick. The total gas pressure is an important factor for the synthesis of the large-scale centimeter-long alpha-Si3N4 nanowires, which can easily adjust the pressure of the vapors to supersaturation condition. The growth of the nanowires was governed by the vapor-solid mechanism. The alpha-Si3N4 nanowires showed an intensive blue light emission centered at 450 nm at room temperature, which arise from the recombination between the intrinsic conduction band edge and Si dangling bonds.