We investigated the effect of temperature on the growth rate and structure of carbon nanotubes using scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The carbon nanotubes were grown vertically aligned on iron nanoparticle deposited silicon substrate by thermal chemical vapor deposition of acetylene in the temperature range 800-1100 °C. As the growth temperature increases from 800 to 1100 °C, the average diameter increases from 20 to 150 nm and the growth rate also increases by about 20 times. All carbon nanotubes exhibit a bamboo-like structure over this temperature range. In the carbon nanotubes grown at higher temperature, the thicker compartment layers appear more frequently. The relative amount of crystalline graphitic sheets increases progressively with the growth temperature. The Arrhenius plot provides the activation energy of carbon nanotube growth to be at least 30 kcal/mol. The results indicate that the bulk diffusion of carbons would be an important factor in the growth of carbon nanotubes.

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.

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Gallium oxide nanowires were synthesized via chemical vapor deposition of gallium/gallium oxide mixture and oxygen. The diameter of the nanowires is 30−80 nm with an average value of 50 nm. They consist of single-crystalline monoclinic crystal. While the nanowires grown without catalyst exhibit a significant planar defect, the nanowires grown with nickel catalytic nanopaticles are almost defect-free. The growth direction of the nanowires grown without the catalyst is uniformly [010]. In contrast, the nanowires grown with the catalyst have random growth direction. X-ray diffraction, Raman spectroscopy, and photoluminescence are well correlated with the structural characteristics of the nanowires. The result provides an evidence for the catalyst effect in controlling the structure of nanowires.

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