Sulfur-assisted growth of silicon nanowires using the VLS method

The synthesis of single-crystal silicon (Si) nanowires by a metal-catalyst-free vapor-liquid-solid (VLS) process has been studied. Si nanowires have been successfully synthesized by a simple thermal treatment without using a metal catalyst, while well-aligned nanowires have been grown by the conventional Au-catalytic VLS process. It is thought that sulfur, rather than metals, plays an important role in this synthesis technique, which is distinct from the conventional metal-catalytic VLS process. For the case without metal catalysts, single-crystal Si nanowires are grown by a VLS process in which the silicon sulfides produced by a reaction between Si and sulfur act as both molten eutectic alloy droplets and the source gases for nanowire growth. Structural characterizations of the nanowires were performed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The XRD measurements showed that the single crystal nanowires on a (111)-oriented Si substrate were preferentially oriented in a <;111> growth direction.