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The self-synthesis of tungsten oxide (W18O49) nanowires on sputter-deposited W films prepared under different O2/Ar flow rate ratios (OAFRRs) in the sputtering gas is reported. After thermally annealing at 700?850??C in N2 ambient for 15?min, dense and well crystalline W18O49 (010) nanowires or nanobelts were obtained depending on the oxygen content in the sputtering gas. Experimental results show that the annealing temperature required for the full growth of W18O49 nanowires reduced when the OAFRR in the sputtering gas was increased. It is found that the oxygen absorbed in the surface region is responsible for the growth of nanowires. As the OAFRR was increased to (8?sccm)/(24?sccm), which resulted in a saturated oxygen content of about 55 at.% inside the W film, large-scale nanobelts or nanosheets of W18O49 were grown. The possible growth mechanism which governs the evolution from nanowires to nanobelts as the OAFRR was changed is also discussed.

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.

The self-synthesis of tungsten oxide (W18O49) nanowires on sputter-deposited WCx films using a simple annealing/oxidization process was reported. It was found that thermal annealing of WCx films at 680°C for 30min in nitrogen followed by oxidation at 450°C for 30min in pure oxygen would yield dense and well-crystallized monoclinic W18O49 (010) nanowires with a typical length/diameter of about 0.15–0.2μm∕10–20nm. The formation of W18O49 nanowires is attributed to the nuclei of immature W2C nanowires experiencing a regrowth process, accompanied by carbon depletion and the oxidization of tungsten during the subsequent oxidization process.