Unveiling low-temperature thermal oxidation growth of W ₁₈ O ₄₉ nanowires with metastable β-W films

With features of innate tunnels and oxygen vacancies derived from a unique geometrical structure and sub-stoichiometric compositions, W₁₈O₄₉ nanowires have been explored as multifunctional materials with diverse applications. Though thermal oxidation offers a facile method to synthesize patterned W₁₈O₄₉ nanowires, the relatively high growth temperature (≳500 °C) hinders their emerging applications in flexible or wearable electronics. In this work, aiming to lower the growth temperature of W₁₈O₄₉ nanowires by thermal oxidation, the temperature and oxygen partial pressure dependent growth has been systematically investigated for both W films and powders. W₁₈O₄₉ nanowires could be steadily obtained with appropriate temperature and oxygen pressure ranges for both cases, while the growth temperature of a W film (metastable β phase dominant) could be much lower than that of W powder (α phase). The structural analysis indicates that metastable β-W is susceptible to oxidation in comparison with α-W and thus generates oxidation-induced chemical compression for nanowire growth. The growth temperature of W₁₈O₄₉ nanowires could be reduced to ca. 400 °C, which paves the way for the in situ patterning of W₁₈O₄₉ nanowires on indium-tin-oxide (ITO) glass substrates and flexible substrates.