Growth control of carbon nanotubes using nanocomposite nickel/carbon thin films

Recent papers have demonstrated that the growth of carbon nanotubes (CNTs) by plasma enhanced chemical vapor deposition (PECVD) was possible using nanocomposite nickel/carbon (nc-Ni/C) thin films as catalysts. In this study, the growth of CNTs by PECVD in H2/C2H4 atmosphere was achieved using nc-Ni/C thin films deposited by a hybrid plasma process combining the sputtering of a nickel target and the deposition of hydrocarbon by PECVD using Ar/CH4 atmosphere. In order to identify the most favorable conditions to obtain dense CNTs arrays using nc-Ni/C thin films, the Ni content in the catalyst as well as the growth conditions of the CNTs were varied. Films containing 40, 55 and 65at.% of Ni were selected for this study. The growth temperature of the CNTs was varied between 500 and 700°C whereas the electrical power applied to the PECVD source was tuned from 30 to 50W. Scanning electron microscopy and Raman spectroscopy were employed to probe the morphology and the structure of the CNT's. Depending on the chemical composition of the nc-Ni/C thin films, different trends were observed. No CNTs were obtained neither for the highest nickel content (i.e. %Ni=65at.%) nor for the lowest growth temperature (i.e. 500°C). On the other hand, for temperatures exceeding 500°C, while a high power on the PECVD source (i.e. 50W) was found to be necessary to obtain CNTs in the case of films with a moderate Ni content (i.e. %Ni=55at.%), a lower power (i.e. 30W) was sufficient for the film with the lowest Ni content (i.e. %Ni=40at.%). This difference in behavior was attributed to the differences in microstructure of nc-Ni/C thin films which is directly related to their chemical composition.