A simple method for the large-scale synthesis of gram quantities of compound semiconductor nanowires without the need for any external catalysts or templates is presented. This method is demonstrated using zinc phosphide (Zn3P2) and zinc antimonide (β-Zn4Sb3) nanowires as example systems. Large-scale synthesis of Zn3P2 and Zn4Sb3 nanowire powders was accomplished using a hot-walled chemical vapor deposition chamber by transporting phosphorus and antimony, respectively, via the vapor phase onto heated zinc foils. The zinc foils were rolled concentrically into coils to maximize the substrate surface area, and consequently, the nanowire yield. Using this method, 250 mg of Zn3P2 nanowires were obtained on 480 cm(2) of zinc foil in a span of 45 minutes. Furthermore, a process of exposing the synthesized nanowires to a vapor of organic functional molecules immediately after their synthesis and before their removal from the vacuum chamber was developed to obtain large quantities of surface functionalized nanowire powders. This in situ vapor-phase functionalization procedure passivated the nanowire surfaces without adversely affecting their morphology or dimensions. Our studies revealed that both 4-aminothiophenol and 3-propanedithiol functionalized Zn3P2 nanowires were stable over a 120 day duration without any agglomeration or degradation. This method of mass producing nanowires can also be extended to other binary semiconductors.

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 Mg2Si 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 Mg2Si 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 Mg2Si 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.

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A simple and reliable strategy for stabilizing the surfaces of compound semiconductors was presented. The strategy involved decorating the surfaces of compound semiconductor nanowires non-conformally with small molecules of boron nitride (BN). More specifically, Zn3P2, ZnO and Mg2Si nanowires, highly useful in energy conversion device fabrication (e.g., photovoltaics and thermoelectrics), have been stabilized against air- and acid-assisted degradation by decorating their surfaces with small molecules of BN. It is believed that the decoration of the nanowire surfaces with BN molecules made the nanowire surfaces non-wettable to water and aqueous acid solutions, and thereby imparted them enhanced resistance against water- and acid-assisted degradation. This procedure did not alter the bandgap of the nanowires. Moreover, this procedure aided in retaining the electrical conduction between the nanowire interfaces when the nanowires are assembled into mats or pellets. This strategy solves one of the primary bottlenecks in the widespread use of nanowires in energy conversion device fabrication, namely their stability. It is believed that this strategy is applicable for stabilizing other compound semiconductor nanowires, including nitrides, sulfides, silicides and antimonides.