Synthesis and characterization of iron silicon boron (Fe₅Si ₂B) and iron boride (Fe₃B) nanowires

Single-crystal iron silicon boron (Fe₅Si₂B) and iron boride (Fe₃B) nanowires were synthesized by a chemical vapor deposition (CVD) method on either silicon dioxide (SiO₂) on silicon (Si) or Si substrates without introducing any catalysts. FeI₂ and BI₃ were used as precursors. The typical size of the nanowires is about 5-50 nm in width and 1-20 μm in length. Different kinds of Fe-Si-B and Fe-B structures were synthesized by adjusting the ratio of FeI₂ vapor to BI₃ vapor. Single-crystal Fe₅Si₂B nanowires formed when the FeI₂ sublimator temperature was kept in the range of 540-570 °C. If the FeI₂ sublimator temperature was adjusted in the range of 430-470 °C, single-crystal Fe₃B nanowires were produced. Fe₃B nanowires grow from polycrystalline Fe ₅SiB₂ particles, while Fe₅Si₂B nanowires grow out of the Fe₅Si₂B layers, which are attached to triangle shaped FeSi particles. Both the ratio of FeI₂ vapor to BI₃ vapor and the formation of the particles (Fe ₅SiB₂ particles for the growth of Fe₃B nanowires, FeSi particles for the growth of Fe₅Si₂B nanowires) are critical for the growth of Fe₃B and Fe ₅Si₂B nanowires. The correct FeI₂ vapor to BI₃ vapor ratio assures the desired phase form, while the particles provide preferential sites for adsorption and nucleation of Fe₃B or Fe₅Si₂B molecules. Fe₃B or Fe ₅Si₂B nanowires grow due to the preferred growth direction of 〈110〉.