Silicon nanowires and silica nanoitubes seeded by copper nanoparticles in an organic solvent

Crystalline silicon (Si) nanowires were synthesized by adding copper sulfide (CuS) nanocrystals and monophenylsilane (MPS) to supercritical toluene at 500 degrees C at 10.3 MPa. When a small amount of water and oxygen is added to the reaction, amorphous SiO2 nanotubes form. In both the nanotube and nanowire reactions, the CuS nanocrystals converted to Cu metal. Because the growth temperature is several hundred degrees below the Cu:Si eutectic temperature at 800 degrees C, the nanowires and nanotubes both appear to grow by a solid-phase seeding process. Furthermore, a portion of the SiO2 nanotubes (similar to 5%) were found to be helically coiled. When gold (Au) nanocrystals were added instead of CuS, only SiO2 nanofibers with solid cores formed and there were no coiled structures. The silica/metal interface morphology was examined for both Cu and Au and found to differ significantly for each metal, which perhaps explains the difference in silica morphology produced by these two metals.