VO2nanosheets exhibiting a well-defined metal–insulator phase transition

Abstract

The ultrafast first-order metal–insulator phase transition in VO₂ is characterized by a several orders of magnitude change in optical transmittance and electrical conductivity, which makes this material an attractive candidate for use in a wide variety of applications ranging from Mott field-effect transistors to thermochromic coatings and optical waveguides. However, relatively little progress has been achieved in fabricating VO₂nanostructures exhibiting a well-defined metal–insulator transition despite the potential attractiveness of such structures as building blocks for novel nanoscale electronic devices. Herein, we present a solution-based approach for the synthesis of monoclinic single-crystalline VO₂nanosheets exhibiting a well-defined metal–insulator phase transition by combining the facile hydrothermal reduction of V₂O₅, an inexpensive and abundant precursor, with an annealing process. The controlled hydrothermal reduction of bulk V₂O₅ using small molecule aliphatic alcohols and ketones as reducing agents yields metastable nanostructures of VO₂(B) that can be readily transformed to monoclinic VO₂ exhibiting a sharp metal–insulator phase transition via an annealing process. The morphology and size of the obtained VO₂nanostructures are found to depend on the reaction time and concentration of the added structure-directing agent, providing substantial insight into the nanowire formation process.