ZnO-Templated Synthesis and Metal-Insulator Transition of VO₂ Nanostructures

Vanadium dioxide (VO₂) exhibits a metal-insulator transition (MIT) that is accompanied by steep changes in electrical and optical properties, making it an important component of device architectures that require facile switching between metal and insulating states. VO₂ nanostructures are particularly useful components of such devices, given their unique size-dependent properties and processing capabilities. Here, we show that VO₂ nanostructures can be synthesized by chemical transformation of ZnO nanoparticles, which are readily available and serve as morphological templates. Commercially available and colloidally synthesized ZnO nanoparticles react with VOSO₄ in water at room temperature to form amorphous VO₂, which can be crystallized to the switchable M1 phase of VO₂ upon thermal annealing. Experiments probing various particle dimensions, shapes, surface ligands, and reaction parameters suggest that the reaction occurs by depositing VO₂ on the ZnO particles, which serve as a sacrificial template. The ZnO-derived VO₂ nanostructures exhibit reversible structural transformations between the metallic (R-VO₂) and insulating (M1-VO₂) phases. Dopants such as Al³⁺, which modify both the VO₂ phase and the MIT properties, can be incorporated. The transition temperature also varies with particle size and reaction parameters. Synthesizing VO₂ in solution using ZnO as a sacrificial template provides a potentially scalable route to diverse VO₂ nanostructures that exhibit metal-insulator transitions.