VO2 nanosheets exhibiting a well-defined metal-insulator phase transition

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 VO2 nanostructures 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 VO2 nanosheets 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 VO2 nanostructures are found to depend on the reaction time and concentration of the added structure-directing agent, providing substantial insight into the nanowire formation process.