Role of annealing temperature on the sol-gel synthesis of VO 2 nanowires with in situ characterization of their metal-insulator transition.

Among the techniques to create VO 2 nanostructures, the sol-gel method is the most facile and benefits from simple, manipulable synthetic parameters. Here, by utilizing various TEM techniques, we report the sequential morphological evolution of VO 2 nanostructures in a sol-gel film spin-coated on a customized TEM grid, which underwent oxygen reduction as the annealing temperature increased. In situ TEM dark-field imaging and Raman spectroscopy allowed us to confirm the sharp phase transition behavior of an individual nanowire by illustrating the effect of electrode-clamping-induced tensile stress on the nucleation of the R phase from the M1 phase. The electrical transport properties of a single-nanowire device fabricated on a customized TEM grid showed excellent control of the stoichiometry and crystallinity of the wire. These results offer critical information for preparing tailored VO 2 nanostructures with advanced transition properties by the sol-gel method to enable the fabrication of scalable flexible devices.