Effective patterning of metal nanoparticles on sapphire surface for aligned growth of single-walled carbon nanotubes

We studied patterning of metal nanoparticle catalyst on sapphire (alpha-Al2O3) substrates to grow horizontally-aligned single-walled carbon nanotubes (SWNTs) from defined positions. Various modifications of sapphire surface were investigated for effective adsorption of iron oxide nanoparticles. We found that phosphoric acids bind to sapphire surface and enhance the adsorption of the nanoparticles. This surface modification enabled effective patterning of nanoparticle via electron beam lithography. The small nanoparticles with a mean diameter of 5 nm tended to diffuse at high temperature during the nanotube growth, while the large particles with 12 nm mean diameter mostly stayed at the same position giving aligned SWNTs grown from the catalyst pattern.