Unveiling low-temperature thermal oxidation growth of WO nanowires with metastable β-W films.

With features of innate tunnels and oxygen vacancies derived from a unique geometrical structure and sub-stoichiometric compositions, WO nanowires have been explored as multifunctional materials with diverse applications. Though thermal oxidation offers a facile method to synthesize patterned WO 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 WO nanowires by thermal oxidation, the temperature and oxygen partial pressure dependent growth has been systematically investigated for both W films and powders. WO 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 WO nanowires could be reduced to . 400 °C, which paves the way for the patterning of WO nanowires on indium-tin-oxide (ITO) glass substrates and flexible substrates.