Synthesis mechanism of SiC-SiO2 core/shell nanowires grown by chemical vapor deposition

Core-shell SiC-SiO2 nanowires were grown on silicon substrate with the chemical vapor deposition method using iron nitrate as promoter for the growth and CO as a carbon precursor, under atmospheric pressure and at a temperature of 1100 degrees C. The whole process involves two main stages: promoter conditioning (dewetting) and growth, by reaction with CO. The dewetting phase has been characterized by SEM and TEM techniques, x-ray diffraction and Raman spectroscopy. The results show that at the operating temperature, a solid-state reaction between the substrate and the promoter takes place with the formation of alpha-FeSi2. The growth of the nanowires begins after an induction time of about 5 min from the introduction of CO. The experimental data have been interpreted by considering a nucleation process involving a reaction between FeSi2 and CO. For the nanowires growth phase, a mechanism based on the Vapor-Liquid-Solid theory is proposed, compatible with the morphology of the drop-shaped particles present on the tip of the nanowires.