Effects of Ni catalyst-substrate interaction on carbon nanotubes growth by CVD

An investigation of the effects of substrate type and various treatments on carbon nanotubes (CNT) growth, using an evaporated Ni thin film as a catalyst, is presented. Barrier layers Of SiO2, Si3N4, and TiN on Si were used as substrates. The catalyst-insulating substrate systems have been processed in several gaseous atmospheres (Ar, NH3 and H-2) and in the temperature range 700-900 degrees C, in order to obtain the most appropriate morphology, size and density of catalyst particles as seeds for the subsequent CNT growth. On this kind of substrates, the smallest nanoparticles were obtained on SiO2 layers, in H-2 or NH3 atmosphere even at 700 degrees C. However, the best vertically aligned and well-graphitized CNT resulted from the NH3 annealing process, followed by the CNT deposition at 900 degrees C in C2H2 and H-2. On TiN conducting substrates, the best vertically aligned CNT were deposited using a shorter annealing step and a deposition process at reduced pressure. The samples were characterized by means of scanning electron microscopy (SEM) and Raman spectroscopy analysis.