Chemical functionalization of single walled carbon nanotubes q Urszula Dettlaff-Weglikowska a, * , Jean-Michel Benoit a,d , Po-Wen Chiu a , Ralf Graupner b , Sergey Lebedkin c , Siegmar Roth a a Max-Planck-Institute for Solid State Research, Heisenbergstr. 1, D-70569 Stuttgart, Germany b Institute of Technical Physics, University of Erlangen, Erwin-Rommel-str.1, D-91058 Erlangen, Germany c Institute of Physical Chemistry, University of Karlsruhe, Keizer str. 12, D-76128 Karlsruhe, Germany d Laboratoire de Physique Cristalline, IMN, Universit e de Nantes, BP 32229, F-44322 Nantes Cedex 3, France Received 8 May 2002; accepted 17 September 2002 Abstract Chemical modification has been performed on purified single walled carbon nanotubes. XPS spectrum shows that the peak corresponding to C (1s) centered at 284.38 eV in pure nanotubes (graphitic C) is 0.4 eV downshifted in chlorinated sample. Sub- sequent coupling reactions were carried out with diamine molecules to form intertube connections. Tripropylentetramine and phenylendiamine have been chosen as a molecular linker. End-to-side and end-to-end nanotube interconnections are formed and then observed by atomic force microscopy (AFM). Statistical analysis made from AFM images shows around 30% junctions in functionalized and less than 2% in pristine material. Remarkable features can be observed in the Raman spectra at different functionalization steps. Simple conductance measurements on bucky papers prepared from prestine nanotubes and from nanotubes modified at various steps have been made and are discussed. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 61.46.þw Keywords: Single wall carbon nanotubes; Functionalization; Fullerenes; Derivatives 1. Introduction Chemical functionalization of single walled carbon nanotubes (SWNTs) is essential for many applications. Attachment of functional groups or aliphatic carbon chains to the nanotubes can dramatically increase the solubility of nanotube material. Chemical modified carbon nanotubes can easily be fixed on a surface via chemical bonds from the surface to the nanotube. Or- ganic molecules like dyes, proteins or nucleic acids may be coupled with functionalized nanotubes for sensor applications. Side wall functional groups should react with polymers and improve the mechanical properties of nanocomposites. Tubes interconnected by chemical bonds will have a reduced contact resistance in con- ducting and transparent layers. Furthermore, chemical modification should avoid bundeling and increase the specific surface area for gas, in particular for H 2 ad- sorption. Even for interconnection purposes in nano- scale circuits, suitable functionalization provides an attractive method to link individual tubes to form more complex networks. 2. Experimental SWNTs used in our experiments were produced at the University of Karlsruhe, Germany by laser ablation of carbon target containing 1.2 at.% Ni and 1.2 at.% Co as catalysts, or by high pressure CO disproportionation over Fe catalyst (HiPco) at CNI, Houston, USA. The raw samples were purified by controlled thermal oxi- dation in air followed by sonication in HCl [1]. As prepared SWNTs (0.4 g) were sonicated in conc. HCl for 15 min. After filtration and washing with water the black solid was heated at 225 °C for 18 h. The metal im- purities were removed by HCl extraction. The thermal Current Applied Physics 2 (2002) 497–501 www.elsevier.com/locate/cap q Original version presented at QTSM & QFS Õ02 (Multilateral Symposium between the Korean Academy of Science and Technology and the Foreign Academies), Yonsei University, Seoul, Korea, 8–10 May 2002. * Corresponding author. E-mail address: u.dettlaff@fkf.mpg.de (U. Dettlaff-Weglikowska). 1567-1739/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII:S1567-1739(02)00164-5