Growth Mechnism of Carbon Nanotubes

1991年以后，我们明确了在大气中用直流电弧法蒸发石墨棒作为阴极沉积可以制备多壁碳纳米管。当改变大气气体种类时，通过扫描电子显微镜和透射电子显微镜可以观察到不同的形貌。当我们使用纯氢气作为大气气体时，可以得到高质量的多壁碳纳米管，其中共存的碳纳米颗粒较少(1997)。因此，如果共存的碳纳米颗粒最初较少，则很容易去除共存的碳纳米颗粒并进行提纯。事实上，我们可以通过简单的物理方法得到纯化的多壁碳纳米管，即用500ﾟC的红外辐射加热器在空气中照射30min，当我们在纯氢气中蒸发石墨电极时，我们可以得到内径为1.0 nm的极窄的多壁碳纳米管。内管周围是等间距的石墨烯薄片，0.34 nm，结晶度高。为了阐明纯氢气体适合制备高质量多壁碳纳米管的原因，我们对弧光放电的光发射进行了分析。因此，大气气体中存在大量的H原子和CH分子，包括H原子，如H2或CH4。尤其是CH分子的存在似乎对石墨烯薄膜的边缘生长有很大的影响。然而，通过对冷却后的气体进行复合分析，没有发现CH分子。

We made clear that multiwalled carbon nanotubes could be prepared by DC arc evaporation of graphite rods in atmospheric gas as cathode deposit, after 1991. When we changed the kind of atmospheric gas, different kinds of morphology could be observed by scanning electron microscopy or transmission electron microscopy. When we used pure hydrogen gas as atmospheric gas, high, quality multiwalled carbon nanotubes with less co-existing carbon nanoparticles could be obtained (1997). Thus, if co-existing carbon nanoparticles were less originally, it is easy to remove co-existing carbon nanoparticles and to purify. In fact, we could get purified maltiwalled carbon nanotubes by simple physical method, namely by irradiating the specimen in air (1998) by infrared radiation heater at 500ﾟC for 30min.When we evaporated the graphite electrode in pure hydrogen gas, we could get maltiwalled carbon nanotubes having extremely narrow inner tube of the diameter 1.0nm in the order. The inner tube was surrounded by graphene sheets of equal distance, 0.34nm, and with high crystalline. In order to clarify the reason why pure hydrogen gas is appropriate for production of high quality multiwalled carbon nanotubes, we analyzed the optical emission of arc discharge. As the result, the existence of much H atoms and CH molecules in atmospheric gas including H atoms, such as H2 or CH4. Especially, it seems that the existence of CH molecules affects strongly for the growth of edge of graphene sheets. However, the CH molecules can not be found by a composite analysis of gas after cooling.