Metal surface nucleated supercritical fluid–solid–solid growth of Si and Ge/SiOx core–shell nanowires

High yields of single-crystalline silicon nanowires and germanium/silicon oxide core-shell nanostructures were synthesized using a supercritical fluid-solid-solid growth mechanism. The formation of the one-dimensional nanostructures was investigated on stainless steel and titanium reactor cell walls. The nanowire growth is diffusion controlled with no catalyst particles being observed at the tip of the nanowires, which is contrary to the characteristic feature of a one-dimensional growth based on the vapor-liquid-solid mechanism. The diameter and length of the nanowires were in the ranges of 30-60 nm and 1-10 µm, respectively, as found by high-resolution electron microscopy. The nanowires were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM).