Synthesis of carbon nanotubes and nanofibers by thermal CVD on SiO2 and Al2O3 support layers.

In this work, catalytic thermal chemical vapor deposition method, using a mixture of methane and hydrogen at atmospheric pressure in a horizontal tubular quartz furnace, was used to grow carbon nanostructured materials. Silicon wafers with SiO2 or Al2O3 layers were used as support for thin nickel film deposition used as catalyst. It has been shown that the interaction between catalysts and substrates is of critical importance for carbon nanotube growth. However, this mechanism is not completely understood. Here, the interaction between catalyst nickel film and two different oxide layers supported on silicon wafers was studied as well as the influence of both support systems (SiO2/Si and Al2O3/Si) on the carbon nanostructures growth at different temperatures and process running times. The substrates were characterized by atomic force microscopy and the carbon nanostructured materials were studied by Raman spectroscopy, high resolution scanning and transmission electron microscopy. At higher temperatures it was observed a high density of carbon nanotubes grown over Al2O3 support layer when compared to SiO2 support layer showing a different behavior for Ni catalyst on each of the substrates. A quite different Ni catalyst behavior was observed at lower temperatures due to the formation of carbon nanofibers instead of carbon nanotubes on both substrates.