Oriented growth of single-walled carbon nanotubes on a MgO(0 0 1) surface

Oriented growth of carbon nanotubes lying on a single-crystal MgO(0 0 1) surface is reported. The nanotubes were grown at 900 °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(0 0 1) plane and preferentially along the two perpendicular directions, [1 1 0] and [11¯0]. 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.