Thermal Evaporation Synthesis of Vertically Aligned Zn₂SnO₄/ZnO Radial Heterostructured Nanowires Array

• Main Authors: Gillsang Han, Minje Kang, Yoojae Jeong, Sangwook Lee, Insun Cho
• Format: Article
• Language: English
• Published: MDPI AG 2021-06-01
• Series: Nanomaterials
• Subjects: thermal evaporation synthesis; Zn₂SnO₄/ZnO; heterostructured nanowires array; interface; charge transport
• Online Access: https://www.mdpi.com/2079-4991/11/6/1500

The construction of a heterostructured nanowires array allows the simultaneous manipulation of the interfacial, surface, charge transport, and transfer properties, offering new opportunities to achieve multi-functionality for various applications. Herein, we developed facile thermal evaporation and post-annealing method to synthesize ternary-Zn₂SnO₄/binary-ZnO radially heterostructured nanowires array (HNA). Vertically aligned ZnO nanowires array (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 nanowires array.