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

Abstract

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 WO_2.9 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 WO_2.9 nanowires by adjusting the Sn²⁺ : Zn²⁺ molar ratio in an aqueous ethylenediamine solution at 65 °C. With WO_2.9 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/WO_2.9 and Zn₂SnO₄/WO_2.9, despite lattice mismatches of >20%.