Research on Precursors of Carbon Nanotubes for Control of Layer Numbers

采用一种新型的高温脉冲弧光放电方法，成功地制备和提纯了直径分布小、缺陷少的高质量双壁碳纳米管。HQDWNTs的外径为1.6~2.0 nm，是目前最窄的双壁碳纳米管之一。这些HQDWNTs具有普通单壁碳纳米管所不存在的层间相互作用，并且具有来自层间相互作用的新颖性质。对于原子级结构，HQDWNTs在内层和外层之间具有相关性。我们发现，内层和外层的手性螺旋倾向于具有相同的手性螺旋，即两层都具有右手或左手结构，并且两层之间存在局部公度的图形堆积。由于其结构的均匀性和壁的石墨化程度不够好，没有观察到与其他多壁碳纳米管的结构相关性。此外，以HQDWNTs为沟道的场效应晶体管的输运特性也表现出特殊的双极性，这也来自于HQDWNTs的层相互作用和结构的均匀性。目前，用于研究单壁碳纳米管和多壁碳纳米管的层间相互作用和电子性质的STM观察正在进行中。如前所述，我们已经成功地控制了单壁碳纳米管和多壁碳纳米管的层数，并揭示了来自层间相互作用的多壁碳纳米管的新性质。进一步的研究正在进行中，以开发一种通过离子迁移率法监测碳纳米管前驱体来控制层数的方法。层数是在毫秒的时间范围内确定的纳米管生长的非常早期的阶段。离子迁移率的测量比传统的透射电子显微镜、原子力显微镜和扫描隧道显微镜等方法要快得多，因此适合于测量。

We have succeeded to produce and purify high-quality double wall carbon nanotubes (HQDWNTs) with low diameter distribution and very few defects by a newly developed high-temperature pulsed arc discharge method. The diameter distribution of HQDWNTs is 1.6〜2.0 nm for the outer diameter, which is one of the narrowest double wall carbon nanotubes at this moment. These HQDWNTs have inter layer interaction, which does not exit in normal single-wall carbon nanotubes (SWNTs), and have novel properties coming from the layer interaction. For the atomic level structures, HQDWNTs have correlation between the inner and the outer layers. We have found that chiral helicities of the inner and the outer layers tend to have the same ones, that is, both layers have right handed or left handed structures, and that there are locally commensurate graphen stacking between the layers. The structural correlations have not been observed with other DWNTs since their structural uniformity and the graphitization of the wall are not good enough for the observations. Furthermore, transport properties of field effect transistors using HQDWNTs as channels also show the special ambipolar properties, which also come from layer interaction and structural uniformity of HQDWNTs. Now STM observation to investigate the layer interaction and details of electronic properties are in progress.As shown previously, we have succeeded to control the number of layers of SWNTs and DWNTs and to reveal the novel properties of DWNTs, which come from the layer interaction. Further researches are in progress to develop a control method for the numbers of layers by monitoring the precursors of carbon nanotubes with ion mobility method. The numbers of layers are determined very early stages of nanotubes growth in the time range of ms. The ion mobility measurements are suitable for the measurements since they are much faster than traditional methods like TEM, AFM and STM.