Bias-enhanced growth of carbon nanotubes directly on metallic wires

Abstract

Carbon nanotubes (CNTs) have been grown directly on metallic wires by apowerful but simple technique, which we call cold-plasma chemical vapourdeposition. The growth occurs on an Fe catalyst supported by kanthal wires whileheating under a hydrocarbon precursor gas and plasma created by a bias. Apossible application for such nanotubes on metallic wires is in luminescent tubes.To realize such devices, it is important to grow the nanotubes with controlleddensity, length, and alignment. In the present investigation we have made asystematic scanning electron microscopy study of these nanotubes. Thegrowth rate for the CNTs is found to be very high. Just a few seconds issufficient for covering a large surface area. Increased growth time leads toenhanced site density of the nanotubes. The diameter of the nanotubesincreases with the growth temperature. CNTs are not always straight; spiralbehaviour is quite often observed. We observed, probably for the firsttime, increase in the spiral periodicity of the nanotubes with increasingtemperature. On applying a high bias to the wire (creating plasma), thenumber of spiral structures was reduced; instead, mostly aligned andself-supporting nanotubes were formed, with lengths as high as 45 μm.