Thermal Evaporation Synthesis of Vertically Aligned Zn2SnO4/ZnO Radial Heterostructured Nanowire Arrays

Abstract The construction of a heterostructured nanowire array allows the manipulation of the interfacial, surface, charge transport, and transfer properties simultaneously, offering new opportunities to achieve multi-functionality for various applications. Herein, we developed a facile thermal evaporation and post-annealing method to synthesize ternary-Zn2SnO4/binary-ZnO radially heterostructured nanowire arrays (HNA). Vertically aligned ZnO nanowire arrays (3.5 μm in length) were grown on a ZnO-nanoparticle-seeded fluorine-doped tin oxide substrate by a hydrothermal method. Subsequently, the amorphous layer consisting of Zn-Sn-O complex was uniformly deposited on the surface of the ZnO nanowires via the thermal evaporation of the Zn and Sn powder mixture in vacuum, followed by post-annealing at 550 °C in air to oxidize and crystallize the Zn2SnO4 shell layer. The use of a powder mixture composed of elemental Zn and Sn (rather than oxides and carbon mixture) as an evaporation source ensures high vapor pressure at a low temperature (e.g., 700 °C) during thermal evaporation. The morphology, microstructure, and charge-transport properties of the Zn2SnO4/ZnO HNA were investigated by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, transmission electron microscopy, and electrochemical impedance spectroscopy. Notably, the optimally synthesized Zn2SnO4/ZnO HNA shows an intimate interface, high surface roughness, and superior charge-separation and -transport properties compared with the pristine ZnO nanowire array.