Avouris P. Tungsten oxide nanowire growth by chemically induced strain

We have investigated the formation of tungsten oxide nanowires under different chemical vapor deposition (CVD) conditions. We find that exposure of oxidized tungsten films to hydrogen and methane at 900 °C 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 to other nanowire systems. Interest in semiconducting nanowires continues to grow, in part, because of their potential in nanoelectronics and optoelec-tronics.1 To date, a wide variety of nanowire-based devices have been demonstrated, including photodetectors, photodiodes, and sensors.2 Nanowires offer certain advantages over planar devices. For example, strain arising from lattice mismatch can be accommodated via radial relaxation, rather than through the creation of bulk dislocations, allowing new types of heterojuc-tions to be formed.3 The high surface/volume ratio can also mak