Bias-enhanced growth of carbon nanotubes directly on metallic wires

Carbon nanotubes (CNTs) have been grown directly on metallic wires by a powerful but simple technique, which we call cold-plasma chemical vapour deposition. The growth occurs on an Fe catalyst supported by kanthal wires while heating under a hydrocarbon precursor gas and plasma created by a bias. A possible application for such nanotubes on metallic wires is in luminescent tubes. To realize such devices, it is important to grow the nanotubes with controlled density, length, and alignment. In the present investigation we have made a systematic scanning electron microscopy study of these nanotubes. The growth rate for the CNTs is found to be very high. Just a few seconds is sufficient for covering a large surface area. Increased growth time leads to enhanced site density of the nanotubes. The diameter of the nanotubes increases with the growth temperature. CNTs are not always straight; spiral behaviour is quite often observed. We observed, probably for the first time, increase in the spiral periodicity of the nanotubes with increasing temperature. On applying a high bias to the wire (creating plasma), the number of spiral structures was reduced; instead, mostly aligned and self-supporting nanotubes were formed, with lengths as high as 45 mum.