Fluorination of multi-walled carbon nanotubes (MWNTs) via surface wave microwave (SW-MW) plasma treatment Golap Kalita a,Ã , Sudip Adhikari a , Hare Ram Aryal a , Dilip Chandra Ghimre a , Rakesh Afre b , Tetsuo Soga b , Maheshwar Sharon c , Masayoshi Umeno a a Department of Electrical and Electronics Engineering, Chubu University,1200 Matsumoto-cho, Kasugai-shi 487-8501, Japan b Department of Environmental Technology and Urban Planning, Nagoya Institute of Technology, Nagoya 4668555, Japan c Nanotechnology Research Center, Birla College, Kalyan 421304, India article info Article history: Received 20 December 2007 Accepted 25 July 2008 Available online 8 August 2008 PACS: 61.46.Fg 81.65.Cf 64.70.Nd Keywords: Carbon nanotubes Surface wave microwave plasma Fluorination Atomic properties Structural properties abstract Here, we report fluorination of multi-walled carbon nanotubes (MWNTs) via the surface wave microwave (SW-MW) plasma technique. We have investigated the change in the atomic and structures properties of fluorinated MWNTs using X-ray photoemission electron microscopy (XPS), Raman spectroscopy and transmission electron microscopy (TEM). The XPS study presents a semi-ionic boding character at a low concentration and a covalent bonding character at a high concentration. The Raman spectroscopy study shows an increase in disordered sp 3 hybridization in MWNTs with fluorine incorporation. High-resolution TEM study of fluorinated MWNTs shows an induced defect on the sidewall without affecting the inner tubes’ structure. & 2008 Elsevier B.V. All rights reserved. 1. Introduction Carbon nanotubes (CNTs) as a form of cylindrical graphitic shells [1,2] have attracted the interest of scientists for its application in the field of nanotechnology such as electronic devices, energy storage application, etc. [3–5]. In spite of intensive research on CNTs, practical applications of CNTs in electronic devices are still limited by a number of reasons. Functionalized CNTs are chemically more reactive and can be used for further processing such as thiolization or for integration into a nano- composite [6–8]. Functionalization of CNTs sidewalls represents a solution in order to improve the interactions between CNTs and the solvent or the polymer matrix and thus increase their dispersion ability [9]. However, the sidewall modification is not easily accessible, since open ends of CNTs are more reactive than the sidewall due to the presence of dangling bonds [10]. There are mainly two different approaches for surface modification of CNTs. One is the noncovalent functionalization, which has been carried out by several processes such as ultra- sonication, addition of surfactants, polymer wrapping, etc. [11–15]. The other approach relies on the covalent grafting of functional groups on the sidewalls of CNTs [16]. Covalent functionalizations of CNTs were achieved by solvent processing, plasma treatment, etc. [17–19]. Among the different techniques, the plasma treatment method is important since it has the advantage of being nonpolluting and due to the possibility of scaling up to produce large quantities necessary for commercial applications. Since fluorination is one of the most effective chemical methods to modify and control physiochemical properties in a wide range, fluorinations of new forms of carbon materials are of great interest [10,20]. There are reports of fluorination of CNTs by plasma treatment and demonstrated sidewall functionalization [21,22]. Fluorination can also enhance the solubility in various solvent and homogeneous composite formations with conducting polymers. Mickelson et al. have also shown in further work that fluorinated single-walled carbon nanotubes (F-SWCNTs) dissolve well in alcohol solvents to yield a long-lasting metastable solution [23]. Fluorination may enhance the wettability of the tubes in a water solvent by inducing a surface dipole layer on the CNTs’ wall [24]. The bonding nature of fluorinated CNTs and the disintegration process upon fluorination are not clearly under- stood and more study is needed on the interaction of fluorine atoms and CNTs. ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/physe Physica E 1386-9477/$ - see front matter & 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.physe.2008.07.015 Ã Corresponding author. Tel.: +81568 511111; fax: +81568511478. E-mail address: golapkalita@yahoo.co.in (G. Kalita). Physica E 41 (2008) 299–303