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We report a heat treatment of catalyst in air that drastically enhances a growth of carbon nanotubes (CNTs) by means of thermal chemical vapor deposition (CVD). An Fe catalyst film deposited on a Si substrate was heat treated at 700°C in air before the acetylene CVD. The growth rate of the CNTs grown with the heat treatment was more than seven times higher than that of growth without the heat treatment. A scanning electron microscopy observation showed that the heat treatment in air promotes a granulation of the Fe catalyst. X-ray photoelectron spectroscopy and reflection high energy electron diffraction analyses showed that the heat treatment in air promotes an oxidation of the catalyst film and formation of Fe2O3 nanoparticles, suggesting that the heat treatment of Fe catalyst in air prevented the formation of Fe silicide that would deactivate the catalyst effect of Fe. The Fe2O3 nanoparticles do not agglomerate and can keep their original particles size. Thus the catalyst can maintain a catalyst activity during CNTs growth and, as a result, gives a growth enhancement of CNTs.

The dynamic behavior and degradation of carbon nanotube field emitters were studied by in situ transmission electron microscopy. The carbon nanotube emitters used for the study were double-wall nanotubes (DWNTs) produced by arc discharge. The DWNTs formed bundles, each of which contained about seven DWNTs. The splitting of a bundle into two branches, forming a “Y” shape, accompanied by an abrupt increase of emission current, was observed in real time. The shortening of bundles, presumably due to Joule heating, was also observed. The maximum emission current from a bundle just before its sublimation was at least 10 µA, which corresponds to 1.4 µA per single DWNT.

Single-walled carbon nanotubes (SWNTs) were prepared by ethanol chemical vapor deposition (CVD), using Co and Mo as metal catalysts deposited on Si/SiO2 substrates with and without an Al underlayer. The effects of Mo addition, catalyst particle size and the Al underlayer were discussed on the basis of the results of scanning electron microscopy (SEM), atomic force microscopy (AFM) and Raman measurement. In substrates with Si/SiO2/Co/Mo structures, a Co layer with a thickness of 1 nm produced smaller catalyst particles and SWNTs with a thinner diameter and at a higher yield than a Co layer with a thickness of 2 nm. The addition of Mo to Co films in substrates was shown to have the effect of suppressing Co aggregation and keeping catalyst particles small, even with high-temperature CVD growth. It was also found that the introduction of an Al underlayer promoted SWNT growth because of the formation of Al2O3 clusters after heat treatment.

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