Combined flame and solution synthesis of nanoscale tungsten-oxide and zinc/tin-oxide heterostructures.

Heterostructures of tungsten–oxide nanowires decorated with zinc/tin–oxide nanostructures are synthesized via a combined flame and solution synthesis approach. Vertically well-aligned tungsten–oxide nanowires are grown on a tungsten substrate by a flame synthesis method. Here, tetragonal WO2.9 nanowires (diameters of 20–50 nm, lengths >10 μm, and coverage density of 109–1010 cm−2) are produced by the vapor–solid mechanism at 1720 K. Various kinds of Zn/Sn–oxide nanostructures are grown or deposited on the WO2.9 nanowires by adjusting the Sn2+ : Zn2+ molar ratio in an aqueous ethylenediamine solution at 65 °C. With WO2.9 nanowires serving as the base structures, sequential growth or deposition on them of hexagonal ZnO nanoplates, Zn2SnO4 nanocubes, and SnO2 nanoparticles are attained for Sn2+ : Zn2+ ratios of 0 : 1, 1 : 10, and 10 : 1, respectively, along with different saturation conditions. High-resolution transmission electron microscopy of the interfaces at the nanoheterojunctions shows abrupt interfaces for ZnO/WO2.9 and Zn2SnO4/WO2.9, despite lattice mismatches of >20%.