Synthesis and growth mechanism of various SiO2 nanostructures from straight to helical morphologies

Taking into account the high demands and applications of amorphous SiO2 in various nanostructured forms, here we have synthesized various nanostructures of SiO2 including nanosprings, straight nanofibers, nanotubes and nanobelts. A simple catalytic chemical vapor deposition (CCVD) technique is developed where Si, SiO2 and graphene capsules are utilized as starting materials. The structural and chemical analysis of the as-prepared nanostructures confirms the amorphous nature of SiO2 and shows the minor existence of SiC, which acts as a growth directing agent for various shapes of SiO2. The electron microscopic observations delineate the morphologies of the as-prepared nanostructures with different shapes i.e. nano-fibers, tubes, springs and belts. It is observed that straight SiO2 fibers having diameter of ∼440 nm are thicker than the fibers (∼220 nm) constructing the nanosprings while the overall helical diameter falls in the range of 530-690 nm. The in-depth structural and morphological studies reveal that the growth mechanism of SiO2 nanostructures is in the vapor-liquid-solid (VLS) growth mode. The unique microstructures with special morphologies straight, helical and hollow shapes make them potential candidate for several functional applications such as nanoelectron-magnetic devices, mechanical sensor system and flexible energy storage devices.