2, Materials Research Institute, State College, Pennsylvania, United States
The M1 form of vanadium dioxide exhibits a reversible first-order metal insulator transition (MIT) at 67 οC and is therefore of significant interest for many nanoelectronics and nano-optics devices applications. Synthetically, however, formation of VO2(M1) nanoparticles is challenging because of the complexity of the V-O phase diagram, which includes several structurally related VO2 polymorphs and VnO2n-1 Magneli phases, as well as the tendency to instead form the metastable (B) phase of VO2, which does not exhibit a MIT above room temperature, during solution growth. VO2 nanoparticle domains have been incorporated into nanoscale heterostructures through solution phase epitaxial growth on the tips of rutile TiO2 nanorods. Four distinct classes of VO2–TiO2–VO2 nanorod heterostructures are accessible by modulating the growth conditions. Each type of VO2–TiO2–VO2 nanostructure has a different insulator-metal transition temperature that depends on the VO2 domains sizes and the TiO2–VO2 interfacial strain characteristics. Incorporating the switchable M1 form of VO2 into solution-synthesized nanoscale heterostructures would enable fundamental studies of the size-dependent MIT transition behavior in VO2 and potentially allow the feature sizes of device architectures that could utilize the abrupt electrical and optical switching capabilities of VO2 to be scaled down to significantly smaller dimensions.