By-product processing of Si₃N₄ saw-tooth nanoribbons during carbon foam processing using pyrolysis-nitridation reactions

Si₃N₄ saw-tooth nanoribbons (SNSNs) have been synthesized via a novel approach involving a by-product pyrolysis-nitridation process during carbon foam manufacturing at 1450 °C. The SNSNs formed are ribbon shaped, 80-750 nm wide, 70-80 nm thick and several micrometres in length. The process simply involved thermal pyrolysis of a powdered mixture containing carbon foam precursors and silicon powder under flowing high-purity nitrogen. Pyrolysis gases rich in silicon, silicon oxide and active nitrogen vapours promoted the subsequent synthesis of the SNSNs over the outer surface of the carbon foams via a vapour-solid mechanism. The crystal structure, morphology, chemical composition, growth mechanism and photoluminescence (PL) properties have been studied. The infrared adsorption of SNSNs exhibited two absorption bands with all the peaks related to the Si-N bonds of the α-Si₃N₄ crystalline structure. X-ray photoelectron spectroscopy measurements further confirmed the chemical composition, with minor impurities such as oxygen and carbon. A single nanoribbon has the same width-to-thickness ratio, suggesting a stable morphology resulting from the reduction of the overall surface energy. Intense PL was observed centred at 2.03, 2.48, 2.62, and 3.01 eV, which resulted from the recombination between the intrinsic conduction band edges and silicon dangling bonds with deep-level or trap-level states.