Synthesis and characterization of one-dimensional WO2 nanorodsa)

One-dimensional (1D) WO2 nanorods were synthesized by hot-filament metal vapor deposition at high-pressure Ar flow without using any catalyst. The 1D WO2 nanorods grew on the roots and were a few micrometers long and 50–100nm wide. The x-ray diffraction pattern shows that the as-synthesized 1D WO2 nanorods are the monoclinic structure in space group P21∕c, and the roots are the β tungsten crystal of the cubic structure in space group Im3m. Field-emission-gun transmission electron microscopy images and selected-area electron diffraction patterns further confirm that the monoclinic 1D WO2 nanorods consist of the (011) planes and preferentially grow along the ⟨01¯1⟩ direction. According to these results, an uncatalyzed vapor-solid process is suggested to be the mechanism of growth of the as-synthesized 1D WO2 nanorods. In comparison with the Raman scattering of three-dimensional WO2 bulk powders, the Raman bands of the 1D WO2 nanorod are blueshifted and narrower, indicating phonon confinement associated with...