MS-2-P-1730 In-Situ Environmental TEM Observation of the Formation of Defects in Growing Carbon Nanotubes
As-grown carbon nanotubes (CNTs) generally have various grown-in defects, such as vacancies, pentagon-heptagon pairs, bending, and irregular interlayer spacing. It is well known that the electronic and mechanical properties of CNTs are affected by these grown-in defects. An understanding of the formation mechanism of the CNT grown-in defects is required for the growth of defect-free CNTs exhibiting ideal properties and CNTs with intentionally induced defects exhibiting modified properties. Recent environmental transmission electron microscope (ETEM) [1] observations of chemical vapor deposition (CVD) growth of CNTs have provided us with knowledge of the growth mechanism. We have clarified that CNTs grow from structurally fluctuating iron carbide Fe3C and iron molybdenum carbide (Fe,Mo)23C6 nanoparticles [2-4]. However, in situ studies on the formation of defects in growing CNTs are limited. In this study, we have elucidated the origin of grown-in defects in CNTs, such as bending, irregular interlayer spacing, change in the diameter, and change in the number of graphitic layers, by in situ atomic-scale ETEM observations of the CVD growth of CNTs [5].
Figure 1 shows the growth of a CNT with a drastic disorder of the interlayer spacing. We also observe large changes in the CNT diameter during growth as shown in Fig. 2. Our ETEM observations clearly demonstrate that deformation of the nanoparticle catalysts during CNT growth triggers the formation of these grown-in defects [5]. The small deformation of nanoparticle catalysts at the interface with CNTs gives rise to the formation of bends and disorder of the interlayer spacing (Fig. 1) in CNTs. The changes in the diameter (Fig. 2) and number of graphitic layers in CNTs are caused by the large protrusion on and shrink deformations of nanoparticle catalysts. Based on the ETEM observations, we will propose the formation mechanism of grown-in defects in CNTs.
References
[1] S. Takeda and H. Yoshida, Microscopy, 62 (2013) 193.
[2] H. Yoshida, S. Takeda, T. Uchiyama, H. Kohno, and Y. Homma, Nano Lett., 8 (2008) 2082.
[3] H. Yoshida T. Shimizu, T. Uchiyama, H. Kohno, Y. Homma, and S. Takeda, Nano Lett., 9 (2009) 3810.
[4] H. Yoshida, H. Kohno, and S. Takeda, Micron, 43 (2012) 1176.
[5] H. Yoshida and S. Takeda, Carbon, 70 (2014) 266.
This work was supported by JSPS KAKENHI Grant Number 24710117.
Fig. 1: Drastic disorder in the interlayer spacing of graphitic layers in a growing CNT from a nanoparticle catalyst [5]. The observation time is shown in the images. |
Fig. 2: Large Change in the diameter of a growing CNT from a nanoparticle catalyst [5]. The lattice images in the nanoparticle catalyst corresponds to a (Fe,Mo)23C6-type structure [3,4]. The observation time is shown in the images. |