Mass production of Silicon and Metal Silicide Nanowires using a combination of electroless etching and phase transformation:
In this project, we have developed a simple, but scalable, method for the mass production of compound semiconductor metal silicide nanowire powders. For accomplishing this task, we have studied the process of phase transformation in nanowires. In the first study, silicon nanowires obtained using electroless etching were phase transformed into Mg2Si nanowires by reacting them with magnesium supplied via the vapor phase. Although the process resulted in the retention of nanowire morphology after silicon was completely converted into Mg2Si, it resulted in the formation of polycrystalline Mg2Si nanowires. The diffusion of magnesium into the silicon nanowires, and its subsequent reaction led to the formation of multiple Mg2Si nuclei inside each nanowire. Further growth of these nuclei is believed to be responsible for the formation of polycrystalline Mg2Si nanowires. More recently, we have modified the process and employed solid-state reaction of magnesium foils with tapered silicon nanowire arrays for obtaining single-crystalline Mg2Si nanowires from single-crystalline Mg2Si nanowires. We believe that this process is useful for the mass production of many metal silicide nanowire thermoelectric materials.