Research for in-situ observation technique on solid state carbon nanotube growth and crystal orientation of catalyst.

本研究主要集中在两个方面，一是固体碳纳米管生长的处理和可视化技术的发展，二是扫描透射电镜图像下碳纳米管生长的原位监测分析。我们开发了一种尖端曲率小于5nm的超尖锐探针，以操纵和控制铁催化剂在固态纳米管生长过程中的运动。多壁碳纳米管的场发射通过焦耳加热软化了钨的底部，并且从钨尖端拉出的纳米管的库仑吸引力导致钨探针的尖端具有5纳米的曲率。我们还发现，在低加速电压下，扫描透射电子显微镜（STEM）可以看到探针顶端的局部增强场。利用这些技术，我们研究了铁催化剂迁移到非晶基体中的运动，以阐明催化剂及其晶体的驱动机理。铁催化剂的扩散系数约为0.016 ~ 0.06 m^2/min。估计活化能约为1.8 eV。如果假设催化剂为立方铁碳化合物，则经常观察到形成<100>催化剂// c轴石墨的晶体取向。我们还发现了一种新的石墨化机制，这种机制是在液态Ga的界面表面产生的。在此基础上，我们将进一步发展原位监测和处理技术，加快实现碳纳米管直径和手性的精确控制，以及人工石墨烯基纳米应用的研究。

This research had focused on following two categories, one was development of handling and visualization technique for solid state carbon nanotube growth, and the second was analysis of carbon nanotube growth by means of in-situ monitoring under scanning transmission electron microscope image. We had developed an ultra-sharp probe having less than 5 nm at the tip curvature in order to manipulate and control the movement of iron catalyst during solid state nanotube growth. Field emissions from a multi-walled carbon nanotube soften the bottom of the tungsten by Joule heating, and the coulomb attraction to the nanotube finery pulled off from the tungsten tip resulted in an ultra sharp apex of the tungsten probe having 5 nm in of curvature. We also found that a locally enhanced field at the probe apex can be visualized using scanning transmission electron microscopy (STEM) under low accelerating voltage operation. By using these technique, we investigated the movement of iron catalyst that migrated into an amorphous matrix in order to clarify the driving mechanism of the catalyst and its crystal. The diffusion coefficient of the iron catalyst was found to be about 0.016-0.06 m^2/min. and the activation energy was estimated to about 1.8 eV. If we assume the catalyst was cubic iron-carbon compound, crystal orientation that formed <100> catalyst// c-axis graphite was frequently observed. We also found a new graphitization mechanism that was induced at the interface surface of liquid Ga.Based on those results combining further develop our in-situ monitoring and handling technique, we will accelerate the research toward to realize precision control of diameter and chirality of carbon nanotube, and toward artificial graphene based nano application.