Facile growth of thermochromic VO2 nanostructures with greatly varied phases and morphologies.

We have successfully and reproducibly synthesized a variety of novel vanadium dioxide (VO2) nanostructures, including metastable monoclinic VO2(B) nanoneedles and nanocorals, orthorhombic VO2(O) nanoparticles, and monoclinic VO2(M) nanofacets by manipulating the aging time of a facile sol-gel approach and the subsequent postannealing conditions. We envision that this previously unreported highly controlled synthesis and the resulting distinct morphologies of VO2 will not only provide a promising route for reliably selecting the phase, size, and morphology of these nanostructures, as well as achieving a fundamental understanding of their unusual temperature-dependent optical transmittance, but also facilitate the synthesis of functional VO2 nanostructures for a number of novel applications.