Growth Mechnism of Carbon Nanotubes

1991年以后，我们明确了石墨棒在常压气体中直流电弧蒸发作为阴极沉积可以制备多壁碳纳米管。当我们改变大气气体的种类时，通过扫描电子显微镜或透射电子显微镜可以观察到不同种类的形态。当我们使用纯氢气作为大气气体时，可以获得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，如果原先共存的碳纳米颗粒较少，则很容易去除共存的碳纳米颗粒并进行净化。事实上，我们可以用简单的物理方法得到纯化的多壁碳纳米管，即用红外辐射加热器在500ºC的空气中照射30min（1998）。当我们将石墨电极在纯氢气中蒸发时，我们可以得到内管极窄的多壁碳纳米管，其直径依次为1.0nm。内管被等距0.34nm的高结晶石墨烯片包围。为了阐明纯氢气适合生产高质量多壁碳纳米管的原因，我们对电弧放电的光发射进行了分析。因此，大气中含有H原子的气体如H2或CH4中存在较多的H原子和CH分子。特别是，CH分子的存在似乎对石墨烯片边缘的生长有强烈的影响。然而，通过对冷却后的气体进行复合分析，无法发现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.