Scalable flame synthesis of SiO2 nanowires: dynamics of growth

Abstract

Silica nanowire arrays were grown directly onto plain glass substrates by scalable flamespray pyrolysis of organometallic solutions (hexamethyldisiloxane or tetraethylorthosilicate). The silicon dioxide films consisted of a network of interwoven nanowires froma few to several hundred nanometres long (depending on the process conditions)and about 20 nm in diameter, as determined by scanning electron microscopy.These films were formed rapidly (within 10–20 s) at high growth rates (ca11–30 nm s − 1) by chemical vapour deposition (surface growth) at ambient conditions on the glass substrateas determined by thermophoretic sampling of the flame aerosol and microscopy. In contrast, onhigh purity quartz nearly no nanowires were grown while on steel substrates porousSiO2 films were formed. Functionalization with perfluorooctyl triethoxysilane convertedthe nanowire surface from super-hydrophilic to hydrophobic. Additionally,their hermetic coating by thin carbon layers was demonstrated also revealingtheir potential as substrates for synthesis of other functional 1D compositestructures. This approach is a significant step towards large scale synthesis ofSiO2 nanowires facilitating their utilization in several applications.