Oriented growth of single-walled carbon nanotubes on a MgO(001) surface

Oriented growth of carbon nanotubes lying on a single-crystal MgO(001) surface is reported. The nanotubes were grown at 900 degrees C by chemical vapour deposition using a mixture of carbon monoxide and hydrogen, with Co catalyst nanoparticles formed by self-assembling on MgO under ultra high vacuum conditions. Field emission scanning electron microscopy measurements reveal that the nanotubes grow parallel to the MgO(001) plane and preferentially along the two perpendicular directions, [110] and [110]. The interactions between oxygen atoms of the MgO substrate and carbon nanotubes would drive the directional growth. The Raman spectra support that most nanotubes with a diameter ranging from 1.5 to 4 nm, observed by transmission electron microscopy and atomic force microscopy, are single-walled. The observed directional growth requires a very good surface quality of the MgO substrate. Interestingly, rough areas damaged by water vapour prevent the formation of nanoparticles necessary to the nucleation of nanotubes. (c) 2006 Elsevier Ltd. All rights reserved.