Growth Mechnism of Carbon Nanotubes

1991年以后，我们明确了可以用直流电弧蒸发石墨棒作为阴极存款来制备多壁碳纳米管。当我们改变气氛气体的种类时，可以通过扫描电子显微镜或透射电子显微镜观察到不同的形貌。当我们使用纯氢气作为气氛气体时，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，如果共存的碳纳米颗粒最初较少，则容易去除共存的碳纳米颗粒并进行纯化。实际上，我们可以通过简单的物理方法得到纯化的多壁碳纳米管，即在空气中（1998）用红外辐射加热器在500 ℃下照射样品30min。当我们在纯氢气中蒸发石墨电极时，我们可以得到直径为1.0nm的极窄内管的多壁碳纳米管。内管被等间距的石墨烯片包围，0.34nm，并且具有高结晶度。为了阐明纯氢气适合于制备高质量多壁碳纳米管的原因，我们分析了电弧放电的光发射。其结果是，在含有H原子的大气气体中，如H2或CH4中，存在大量的H原子和CH分子。特别是CH分子的存在对石墨烯片边缘的生长有很大的影响。然而，冷却后的气体的复合分析不能发现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.