Solid-State Phase Transformation as a Route for the Simultaneous Synthesis and Welding of Single-Crystalline Mg2Si Nanowires
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A simple, but elegant, strategy for the simultaneous synthesis and welding of single-crystalline Mg2Si nanowires is presented. For the synthesis of Mg2Si nanowires, the solid-state phase transformation of presynthesized silicon nanowires was employed. For assembling the Mg 2Si nanowires via the formation of Mg2Si bridges, the phase transformation of silica nanoparticle-decorated silicon nanowires was employed. To circumvent the formation of multiple Mg2Si nuclei and hence the phase transformation of single-crystalline Mg2Si nanowires into polycrystalline Mg2Si nanowires, solid-state reaction of silicon nanowire tips with magnesium foils at elevated temperatures of 350-400 C was employed. In this procedure, the supersaturation of the sharp tips of the silicon nanowires with magnesium led to the formation of only one Mg 2Si nucleus per nanowire. Growth of these lone nuclei led to the formation of single-crystalline Mg2Si nanowires. Extension of this procedure for the phase transformation of silica nanoparticle-coated silicon nanowires led to the formation of Mg2Si nanowires with Mg 2Si bridges between them. The formation of Mg2Si bridges was confirmed by high-resolution transmission electron microscopy analysis and further verified by electrical conductivity measurements. Such simultaneous synthesis and assembly of nanowires will be highly useful in the fabrication of thermoelectric modules from not only Mg2Si but also other metal silicide nanowires. 2014 American Chemical Society.