Fabrication of SnO₂ Nanowire Networks on a Spherical Sn Surface by Thermal Oxidation

SnO₂ nanowire networks were synthesized in two steps. Sn spheres (30–800 nm in diameter) embedded in SiO₂ on a Si substrate was synthesized by a chemical vapor deposition method at 700°C. Using the source of these Sn spheres, SnO₂ nanowire (20–40 nm in diameter; 1–10 μm in length) networks on a spherical Sn surface were synthesized by a thermal oxidation method at 800°C through the support of gold. Field emission scanning electron microscopy and high-resolution transmission electron microscopy images indicated that SnO₂ nanowires are single crystalline. In addition, the SnO₂ nanowire is also a tetragonal rutile, with the preferred growth directions along [100] and a lattice spacing of 0.237 nm. Subsequently, the NO₂ sensing properties of the SnO₂ network nanowires sensor at an operating temperature of 50–250°C were examined, and showed a reversible response to NO₂ at various NO₂ concentrations. Finally, a possible formation mechanism of Sn spheres and SnO₂ nanowire networks is also discussed.