Size dependence of optical and mechanical properties of Si3N4 nanobelts controlled by flow rates

Abstract

Single-crystalline Si₃N₄ nanobelts (NBs) were successfully synthesized in a size-controlled manner using graphite, nanosilicon and nanosilica powders in N₂ gas. The average width of Si₃N₄ NBs increased with an increase in the flow rate of N₂ gas, with 264 nm at 50 ml min⁻¹, 295 nm at 100 ml min⁻¹ and 341 nm at 200 ml min⁻¹. The room-temperature photoluminescence (PL) spectra showed that the synthesized α-Si₃N₄ nanobelts with three different sizes all had two strong emission peaks located in the yellow and red spectral range, which could be mainly attributed to the incorporation of a small amount of Al in the NBs, and the larger size could also lead to a slight red shift. The Young's modulus of Si₃N₄ NBs was measured with a hybrid scanning electron microscope/scanning probe microscope (SEM/SPM) system by means of the modulated nanoindentation method. The Young's modulus of Si₃N₄ NBs strongly depended on their size, decreasing from about 548.6 to 455.1 GPa, which can be explained by surface effects and defect-related effects arising due to their nanometer size. These findings provide a method to tailor the optical and mechanical properties of the NBs in a controlled manner over a wide range of Young's modulus values.