Vertically Aligned Carbon Nanotubes Grown by Pyrolysis of Iron, Cobalt, and Nickel Phthalocyanines

Abstract

Carbon nanotubes (CNTs) were grown vertically aligned on silicon oxide substrates by pyrolyzing iron phthalocyanine (FePc), cobalt phthalocyanine (CoPc), and nickel phthalocyanine (NiPc) in the temperature range 700−1000 °C. As the temperature increases from 700 to 1000 °C, the growth rate of CNTs increases by a factor of approximately 45 and the average diameter increases from 30 to 80 nm. The CNTs grown using FePc exhibit about 2 times higher growth rate than those using CoPc and NiPc. The CNTs usually have a cylindrical structure, and a bamboo-like structure with a larger diameter at the higher temperature. The CNTs are doped with 2−6 at. % nitrogen atoms. The nitrogen content tends to decrease with the temperature increase. The CNTs grown using NiPc contain a higher nitrogen concentration compared to those grown using FePc and CoPc. The degree of crystalline perfection of the graphitic sheets increases with the temperature, but depends on the catalyst and the nitrogen content. The Arrhenius plot provides the activation energy 30 ± 3 kcal/mol for all three sources, which is similar to the diffusion energy of carbon in bulk metal. This suggests that the bulk diffusion of carbon plays a decisive role in the growth of CNTs. The strain for the joint between the compartment layer and the wall determines the structure of the CNTs.