Combined Flame and Solution Synthesis of Nanoheterostructures

S.D. Tse
Rutgers University, US

Keywords: nanoparticle synthesis & applications

Summary:

Nanoheterostructures are fabricated by decorating/coating tungsten-oxide nanowires with other materials using a combined flame and solution synthesis method. First, vertically well-aligned single-crystal tungsten-oxide nanowires are grown directly on tungsten substrates via a flame synthesis method. Here, WO2.9 nanowires are produced by the vapor-solid mechanism, with gas phase species (O2, H2O, CO2, and H2) and local gas phase temperature (1720K) specified at the substrate for desired growth, e.g. diameters of 20-50nm, lengths > 10µm, and coverage density of 109-1010cm-2. Then, using aqueous solutions, various kinds of ZnO/SnO2 nanostructures are grown on the WO2.9 nanowires. With WO2.9 nanowires serving as the scaffold, sequential growth of hexagonal ZnO nanoplates, Zn2SnO4 nanocubes, and SnO2 nanoparticles are attained for different Zn2+:Sn2+ concentration ratios. High-resolution transmission electron microscopy (HRTEM) of the interfaces at the nanoheterojunctions show atomically abrupt interfaces for ZnO/WO2.9 and Zn2SnO4/WO2.9, despite lattice mismatches. Separately, using ionic-liquid solutions, single-crystal nanoscale Al layers are electrodeposited on the surfaces of WO2.9 nanowires. These tungsten-oxide/aluminum coaxial nanowire arrays constitute thermite nanocomposites with high reactivity. Such geometry not only presents an avenue to tailor heat-release characteristics due to anisotropic arrangement of fuel and oxidizer, but also possibly eliminates or at least minimizes the presence of an Al2O3 passivation film between the aluminum and metal oxide.