Growth of aligned carbon nanotubes by biasing during growth

Well aligned multiwalled carbon nanotube (CNT) growth was achieved by posit ively biasing the substrate during growth. Growth was performed in a flowin g mixture of 7% CH4 in Ar onto Co covered Si held at 800 degreesC with and without the presence of an electric field. High resolution scanning electro n microscopy shows that the tube alignment occurs only when a positive bias is applied to the substrate whereas no aligned growth occurs under a negat ive bias and no tube growth is observed, under the presently applied condit ions, with no field. This finding may open up the possibility of realizing cold electron emitting devices based on CNTs with a large electric field en hancement. In particular, it may be possible to utilize the same gate which is needed to turn the device on also to obtain field assisted aligned carb on nanotube growth into the desired regions. Alternatively, due to the fact that no CNTs grow under the conditions of this experiment without bias, se lected area biasing may permit selected area growth of vertically aligned c arbon nanotubes, a process that may find many applications. (C) 2001 Americ an Institute of Physics.