Selective Oxidation on Metallic Carbon Nanotubes by Halogen Oxoanions Seon-Mi Yoon, † Sung Jin Kim, ‡ Hyeon-Jin Shin, † Anass Benayad, † Seong Jae Choi, † Ki Kang Kim, ‡ Soo Min Kim, ‡ Yong Jin Park, ‡ Gunn Kim, ‡ Jae-Young Choi,* ,† and Young Hee Lee* ,‡ Display DeVice & Processing Lab and Analytical Engineering Center, Samsung AdVanced Institute of Technology, Post Office Box 111, Suwon 440-600, Korea, and Department of Physics, Department of Nanoscience and Nanotechnology, and Center for Nanotubes and Nanostructured Composites, Sungkyunkwan AdVanced Institute of Nanotechnology, Sungkyunkwan UniVersity, Suwon 440-746, Korea Received September 27, 2007; E-mail: jaeyoung88.choi@saumsung.com (J.-Y.C.); leeyoung@skku.edu (Y.H.L.) Abstract: Chlorine oxoanions with the chlorine atom at different oxidation states were introduced in an attempt to systematically tailor the electronic structures of single-walled carbon nanotubes (SWCNTs). The degree of selective oxidation was controlled systematically by the different oxidation state of the chlorine oxoanion. Selective suppression of the metallic SWCNTs with a minimal effect on the semiconducting SWCNTs was observed at a high oxidation state. The adsorption behavior and charge transfer at a low oxidation state were in contrast to that observed at a high oxidation state. Density functional calculations demonstrated the chemisorption of chloro oxoanions at the low oxidation state and their physisorption at high oxidation states. These results concurred with the experimental observations from X-ray photoelectron spectroscopy. The sheet resistance of the SWCNT film decreased significantly at high oxidation states, which was explained in terms of a p-doping phenomenon that is controlled by the oxidation state. 1. Introduction Modification of the atomic and electronic structures of carbon nanotubes is a crucial step in many applications. 1 Strong chemical bonding between the host materials and carbon nanotubes is essential for enhancing the mechanical properties of the host materials, whereas a simple dispersion of nanotubes in a host matrix can enhance the conductivity of the host materials. 2 Functionalization of single-walled carbon nanotubes (SWCNTs) by hydrogenation and fluorination leads to a significant change not only in the atomic structures but also in the electronic structures of carbon nanotubes. 3,4 Doping control of carbon nanotubes by various chemical means is also strongly dependent on the types of chemical dopants. 5 Various dispers- ants have been used to disperse carbon nanotubes. This often involves serious modification of the electronic structures of the carbon nanotubes. 1 The presence of functional groups in the dispersant may induce a permanent or an induced dipole moment in a molecular solvent. This presumably involves charge transfer between the absorbates and carbon nanotubes, which modifies the electronic structures of the carbon nanotubes. In order to tailor the electronic structures of carbon nanotubes to a desired direction, it is essential to understand the effect of the absorbates. Halogen oxoanions are a systematic oxidant in engineering redox reactions due to the existence of different oxidation states. As the oxidation state of the halogen oxoanions increases, the number of electrons participating in its redox reaction increases, whereas the redox potential of the reaction decreases. 6 Most oxidants can be used as a p-dopant in carbon nanotubes. For example, SOCl 2 , iodine, and a simple acid treatment enhance the majority carrier concentration and increase the conductivity of carbon nanotubes (CNTs). 7-10 This trend can be altered depending on the physisorption or chemisorption states of the adsorbates. Nevertheless, an understanding of the oxidation of CNTs and their related physical and chemical properties are still unclear. Chlorine oxoacids can provide useful information on the doping of CNTs in this matter, which can be engineered by different oxidation states with the same chlorine atoms. In general, a wide range of oxidation states is more easily found in oxidants with chlorine atoms than those with other halogen atoms. 6 Therefore, the effect of oxidation by chlorine oxoanions can be correlated exclusively with the electronic structures of the CNTs. † SAIT. ‡ Sungkyunkwan University. (1) Tasis, D.; Tagmatarchis, N.; Bianco, A.; Prato, M. Chem. ReV. 2006, 106, 1105. (2) Hu, Y.; Shenderova, O.; Hu, Z.; Padgett, C. 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A.; Hu, H.; Haddon, R. C. Nano Lett. 2002, 2, 155. (10) Geng, H.-Z.; Kim, K. K.; So, K. P.; Lee, Y. S.; Chang, Y.; Lee, Y. H. J. Am. Chem. Soc. 2007, 129, 7758. Published on Web 02/02/2008 2610 9 J. AM. CHEM. SOC. 2008, 130, 2610-2616 10.1021/ja077449d CCC: $40.75 © 2008 American Chemical Society