On the thermal annealing conditions for self-synthesis of tungsten carbide nanowires from WC_x films

The thermal annealing conditions in nitrogen ambient for the self-synthesis of tungsten carbide nanowires from sputter-deposited WC_x films were investigated. Experimental results show that the temperature window for the growth of nanowires lies in the range of 500-750°C with the corresponding annealing time interval ranging from 2.5 to 0.25 h. The diameter, length, and density of the grown nanowires are in the range of 10-15 nm, 0.1-0.3 μm, and 210-410 μm^-2, respectively. The degree of carbon depletion in the annealed WC_x films plays a crucial role in determining both the shape and density of the self-synthesized nanowires. Nanowires synthesized at lower temperatures were seen to be smaller in dimension but higher in density. Material analysis reveals that the phase transition from WC to W₂C arising from decarburization of the WC_x film during thermal annealing should be responsible for the self-synthesis of nanowires.