Figure 1. Characterization of W₁₈O₄₉ and annealed WO₃ samples.

(a) X-ray diffraction patterns of as-obtained W₁₈O₄₉ sample and annealed WO₃ with all reflections perfectly indexed; (b) ultraviolet–visible profile comparison between W₁₈O₄₉ sample and annealed WO₃, showing a blue shift and an obvious absorption tail beyond the edge that may arise from the presence of oxygen vacancies; (c,d) scanning electron microscopy images for W₁₈O₄₉ and WO₃ samples, respectively. Inset in (c): high-resolution transmission electron microscopy image on one single nanowire illustrating clear lattice fringe of 0.38 nm, which suggested that the nanowire growth was along the [010] direction.