Synthesis and characterization of tungsten oxide nanorods from chemical vapor deposition-grown tungsten film by low-temperature thermal annealing

A simple thermal annealing was performed to prepare tungsten oxide nanorods directly from tungsten (W) film. The W film was deposited on Si(100) substrate by chemical vapor deposition (CVD) at 450 °C using W(CO)₆. A high density of tungsten oxide nanorods was produced by heating of the W film at 600–700 °C. The morphology, structure, composition, and chemical binding states of the prepared nanorods were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) analysis. XRD and TEM results showed that the grown nanorods were single-crystalline W₁₈O₄₉. According to XPS analysis, the W₁₈O₄₉ nanorods contained ∼55.69% W⁶⁺, ∼32.28% W⁵⁺, and ∼12.03% W⁴⁺. The growth mechanism based on thermodynamics is discussed for the growth of tungsten oxide nanorods from W film.