In Situ Observation of Nucleation and Growth of Carbon Nanotubes from Iron Carbide Nanoparticles
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1142-JJ02-02
In Situ Observation of Nucleation and Growth of Carbon Nanotubes from Iron Carbide Nanoparticles Hideto Yoshida1, Seiji Takeda1, Tetsuya Uchiyama1, Hideo Kohno1, and Yoshikazu Homma2 1 Department of Physics, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan 2 Department of Physics, Tokyo University of Science, Shinjuku, Tokyo, 162-8601, Japan
ABSTRACT Nucleation and growth processes of carbon nanotubes (CNTs) in iron catalyzed chemical vapor deposition (CVD) have been observed by means of in-situ environmental transmission electron microscopy. Our atomic scale observations demonstrate that solid state iron carbide (Fe3C) nanoparticles act as catalyst for the CVD growth of CNTs. Iron carbide nanoparticles are structurally fluctuated in CVD condition. Growth of CNTs can be simply explained by bulk diffusion of carbon atoms since nanoparticles are carbide.
INTRODUCTION Carbon Nanotubes (CNTs) are most important and promising materials for future nanotechnology [1,2]. Recently, the growth methods of CNTs, in particular catalytic chemical vapor deposition (CVD), are developed and therefore we can obtain high purity, vertically aligned CNTs in large quantities [3]. In the CVD growth of CNTs, it is inferred that metal nanoparticles act as catalyst; however the details of the role are still unknown. In order to elucidate the CVD growth mechanism of CNTs including the role of nanoparticle catalysts (NPCs), in-situ observation of the CNT growth is one of the most promising methods [4-9]. In this study, we observe the nucleation and growth of multi-walled CNTs (MWNTs) from NPCs of fluctuating crystalline Fe carbide by atomic-scale in-situ environmental transmission electron microscopy (ETEM) [10]. EXPERIMENT Iron was deposited as a catalyst on silicon substrates with thin SiO2 surface layer by vacuum evaporation. The samples were set in a newly designed ETEM (FEI Tecnai F20 equipped with an environmental-cell) operated at 200 kV. The substrates were heated to 600 ˚C in a vacuum, and then a mixture gas of C2H2:H2 = 1:1 was introduced into the ETEM. The pressure of the gas and the temperature of the substrates in the CVD condition in the ETEM were 10 Pa and 600 ˚C, respectively. The growth of CNTs was recorded at a rate of 1 frame per 0.35 s using a CCD camera. All the images presented in this paper are extracted from in-situ ETEM movies in the CVD condition.
RESULTS AND DISCUSSION Nucleation of MWNTs We have observed the nucleation of a MWNT from a NPC in CVD condition (Fig. 1) [10]. Individual graphene layers can be observed with sufficient spatial resolution. Firstly, graphene layers are formed on an apparent facet of the NPC (Fig. 1a). The graphene layers gradually extend in plane, and bend along the facets of the NPC (Fig. 1b). Additional graphene layers nucleate between the NPC and the existing ones in succession. During this process, the NPC is gradually deformed and a characteristic protrusion appears and extends further (Fig. 1a and 1e). The protrusion sud
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