Transmission Electron Microscopy Study on the Surface Properties of CNTs and Fullerites Exposed to CF 4 Plasma
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1018-EE06-02
Transmission Electron Microscopy Study on the Surface Properties of CNTs and Fullerites Exposed to CF4 Plasma Kaoru Shoda and Seiji Takeda Department of Physics, Graduate School of Science, Osaka University, 1-16 Machikane-yama, Toyonaka, Osaka, 560-0043, Japan
ABSTRACT Various types of CNTs, i.e. single-wall, double-wall, triple-wall, quadruple-wall and multi-wall carbon nanotubes (CNTs), and fullerites were fluorinated in inductive coupled radiofrequency (RF) CF4 plasma at 13.56 MHz, and their structural and bonding properties were investigated by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). We have discussed the correlation between the number of graphene sheets in a CNT and the stability against the fluorination. TEM and XPS analysis clearly state that increase of the number leads to the gain of fluorinated stability. The fluorination of CNTs is initiated at outer tubes and proceeds to inner tubes with increasing RF power, but fluorination depth is limited to only surface area. The fluorination of fullerites forms amorphous layer at the surface, and increases the depth of the layer with RF power.
INTRODUCTION Chemical functionalizaition of carbon nanotubes (CNTs) has been developed for expanding their practical uses since the syntheses of multi-wall carbon nanotubes (MWCNTs) [1] and single-wall carbon nanotubes (SWCNTs) [2] were discovered. For example, oxygen functionalizaition can serve as a purification method for CNTs [3]. Amine groups attached to CNT walls lead to covalent bonds with epoxy resin [4]. CNTs functionalized with a number of functional groups increase in their chemical reactivity, and therefore can be used as a starting point for further processing or integration. Functionalizaition with fluorine group is known to have a potential to expand CNT applications [5]. In addition, it has been expected that sidewall fluorination of SWCNTs may tune their electronic properties that range from insulating over semiconducting to metallic by controlling π-bonding patterns [6,7]. Therefore, the sidewall fluorination could improve the performance in hydrogen storage, secondary battery and supercapacitor. Mickelson et al. [8] fluorinated SWCNTs by direct F2-gas fluorination, and indicated that the product was highly resistive and could survive at temperature up to 325 . However, this method gives higher fluorination rate and deeper penetration into tubes, which makes it difficult to precisely control the fluorination depth from the surface of tubes. Thus, it is needed to develop other methods to access the controllable sidewall fluorination. Plasma technique has a potential to limit fluorination depth to the vicinity of the surface [9]. Moreover, the technique has many advantages; it is a room temperature processing and needs short reaction times as compared to other fluorination methods. Numerous studies have
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been dedicated to investigate the effect of the fluorination on chemical properties of CNTs [1013], but the mechanism is still not well understood
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