The self-synthesis of tungsten oxide ͑W 18 O 49 ͒ nanowires on sputter-deposited WC x films using a simple annealing/oxidization process was reported. It was found that thermal annealing of WC x films at 680°C for 30 min in nitrogen followed by oxidation at 450°C for 30 min in pure oxygen would yield dense and well-crystallized monoclinic W 18 O 49 ͑010͒ nanowires with a typical length/ diameter of about 0.15-0.2 m / 10-20 nm. The formation of W 18 O 49 nanowires is attributed to the nuclei of immature W 2 C nanowires experiencing a regrowth process, accompanied by carbon depletion and the oxidization of tungsten during the subsequent oxidization process.

In this letter, the growth of dense W2C nanowires by a simple thermal annealing of sputter-deposited WCx films in nitrogen ambient is reported. Straight nanowires with a density of 250–260μm−2 and length∕diameter in the range of 0.2–0.3μm∕13–15nm were obtained from the 700°C-annealed samples, which exhibit good electron field emission characteristics with a typical turn-on field of about 1.7V∕μm. The self-catalytic growth of W2C nanowires is attributed to the formation of α-W2C phase caused by carbon depletion in the WCx films during thermal annealing.