The effect of titanium (Ti) added to the top layer of an aluminum (Al)/iron (Fe)/Al (bottom) sandwich catalytic substrate was studied. The Ti caused a significant lengthening in the single-wall carbon nanotube forest produced by chemical vapor deposition (CVD). In general, particles of iron oxide on the Al/Fe/Al catalytic substrate are formed by exposure to the atmosphere during deposition process of the substrate. The particles of iron oxide are metalized during pretreatment under a reductive gas before the growth of the nanotubes with nano-sized dispersion stabilized. On this process, the metallization and the stabilization of nano-sized iron oxide particles occur on the basis of the oxygen affinity in the top aluminum oxide layer, with the ionization tendency Al > Fe. It is thought that the addition of Ti increases the oxygen affinity of the catalytic substrate, since Ti has a stronger ionization tendency than Al. After optimizing the quantity of Ti added to the top layer, we successfully fabricated a millimeter-long, small-diameter, single-wall carbon nanotube forest.
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