Efficient diffusion barrier layers for the catalytic growth of carbon nanotubes on copper substrates

We have investigated the growth of carbon nanotube (CNT) films on copper substrates by the catalytic chemical vapour deposition route. Ferrocene was used as the catalyst precursor and toluene was the carbon feedstock. The copper substrates were coated with nitride and oxide amorphous ceramic barrier coatings in order to prevent diffusion of the iron catalyst during growth. It was found that virtually no CNT grew on pure copper, but long and densely packed mats of CNTs could be grown on TiN-coated copper. Copper substrates coated with SiNx and In2O3:Sn (ITO) also showed better results than pure copper, although the CNT density was much lower than that obtained from TiN/Cu. Auger electron spectroscopy (AES) showed that Fe diffusion occurred into SiNx/Cu and ITO/Cu substrates, which partially inhibited its catalyst activity. In contrast, AES did not detect the presence of diffused Fe into the TiN coating. The estimation of the diffusion coefficient by AES depth profiles for Fe in SiNx, was 3 · 10-3 nm2 s-1. This value establishes an upper limit for Fe diffusion on substrates for proper nanotube nucleation and growth. Secondary ion mass spectrometry provided complementary information on the composition profiles with depth. © 2008 Elsevier Ltd. All rights reserved.