Hot-wire chemical vapor deposition of crystalline tungsten oxide nanoparticles at high density

Tungsten oxide nanostructured rods, particles and occasionally tubes are deposited by heating a tungsten filament in a partial oxygen atmosphere. Transmission electron microscopy (TEM) reveals the nanorods have ∼10-50 nm diameters and ∼50-200 nm lengths. The nanoparticle size ranges from ∼10 to 200 nm. The nanostructures are generally crystalline and predominantly consist of the WO3 monoclinic (I) γ-phase with some monoclinic (II) ε-phase and/or tungsten metal present. Under optimal synthesis conditions, only crystalline nanostructures with a largest dimension of ∼200 nm are observed with TEM analyses. Further characterization conclusively shows that these 'optimal' nanostructures are comprised of only the WO3 monoclinic (I) γ-phase.