  We have investigated the formation of tungsten oxide nanowires under
different CVD conditions. We find that exposure of oxidized tungsten films to
hydrogen and methane at 900C leads to the formation of a dense array of
typically 10 nm diameter nanowires. Structural and chemical analysis shows that
the wires are crystalline WO3. We propose a chemically-driven whisker growth
mechanism in which interfacial strain associated with the formation of tungsten
carbide stimulates nanowire growth. This might be a general concept, applicable
also in other nanowire systems.
