Horizontal single-walled carbon nanotubes on MgO(1Â 1Â 0) and MgO(0Â 0Â 1) substrates

► Preferential alignment of carbon nanotubes along the [11¯0] direction of the MgO(1 1 0) surface. ► Dense alignment of carbon nanotubes along the two orthogonal [1 1 0] and [11¯0] directions of the MgO(0 0 1) surface. ► Distribution of the SWNT diameters grown on MgO(1 1 0) is generally found more narrower than that of SWNT grown on MgO(0 0 1) in the same synthesis conditions. This difference is attributed to the surface energy of MgO(1 1 0) which is twice larger than the one of MgO(0 0 1). Large surface energy would reduce the mobility of Co self-assembled nanoparticles and thus merging between neighbour particles. ► For synthesis at 830 °C, the distribution of the radial breathing mode frequencies of SWNT grown on MgO(1 1 0) is remarkably centered around 142 and 168 cm−1, corresponding to diameters of 1.75 and 1.45 nm. From Kataura plot these SWNTs are semi-conducting.