Electron Microscopic Study of Heat-Treated Carbon Nanotubes

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When carbon nanotrubes were heat-treated under intermediate vacuum (-10^<-4>Torr) at about 250ﾟC by using tungusten heater, all over the surface of carbon nanotubes are coated in complex morphology. It seems like regrowth of carbon nanotubes. The existence of elements, W and O,was confirmed by energy dispersive analytical electron microscope. The reason is that by heating of tungusten heater under low vacuum volatile tungusten oxide was made and it was evaporated to coat the surface of carbon nanotubes. Similar morphology of carbon nanotubes like regrowth was observed in cases of no heat-treating, namely at high arc current or at high pressure of atmospheric gas.Recently, we found that thin and long high quality carbon nanotubes were made by arc discharge evaporation in hydrogen gas. Then, the part of co-existing carbon nanoparticles is also very low and very desirable specimens. if we heat-irra diated the specimens by infrared radiation heating system in air at 500ﾟC for 30 minutes, we could easily removed the co-existing carbon nanoparticles. Namely, thermal purification of carbon nanotubes was realized. Moreover, if the first evaporation by arc discharge for lmin is stable, the orientation of carbon nanotubes is aligned to the parallel direction of electric field. As the result, a bulk of purified carbon nanotubes of 1mm^3 in volume could be obtained. This quantity is fairly much in the order compared with the previous purfication of carbon nanotubes. Therefore, these purified carbon nanotubes are expected in the measurement of physical properties and in practical application.