Microscopic and Spectroscopic Characterization of Paintbrush-like Single-walled Carbon Nanotubes Davide Bonifazi, ² Christophe Nacci, ‡ Riccardo Marega, ² Stephane Campidelli, ² Gustavo Ceballos, ‡ Silvio Modesti,* ,‡,§ Moreno Meneghetti,* ,| and Maurizio Prato* ,² Dipartimento di Scienze Farmaceutiche and INSTM UdR Trieste, UniVersita ` degli Studi di Trieste, Piazzale Europa 1, I-34127 Trieste, Italy, Laboratorio Nazionale TASC-INFM, I-34012 Trieste, Italy, Dipartimento di Fisica, UniVersita ` di Trieste, I-34127 Trieste, Italy, and Dipartimento di Scienze Chimiche, UniVersita ` degli Studi di PadoVa, Via Marzolo 1, I-35131 PadoVa, Italy Received February 20, 2006; Revised Manuscript Received May 5, 2006 ABSTRACT Understanding and controlling the chemical reactivity of carbon nanotubes (CNTs) is a fundamental requisite to prepare novel nanoscopic structures with practical uses in materials applications. Here, we present a comprehensive microscopic and spectroscopic characterization of carbon nanotubes which have been chemically modified. Specifically, scanning tunneling microscopy (STM) investigations of short-oxidized single-walled carbon nanotubes (SWNTs) functionalized with aliphatic chains via amide reaction reveal the presence of bright lumps both on the sidewalls and at the tips. The functionalization pattern is consistent with the oxidation reaction which mainly occurs at the nanotube tips. Thermogravimetric analysis (TGA), steady-state electronic absorption (UV-vis-NIR), and Raman spectroscopic studies confirm the STM observations. Since the discovery of carbon nanostructures, 1 single-walled nanotubes (SWNTs) 2 have attracted much attention as one of the most promising nanomaterials with exceptional electronic and structural properties which led to a variety of applications such as field-emission displays, 3 nanoscale sensors, 4 nanocomposite materials, 5 and electronic circuits. 6-8 However, the lack of solubility and difficult manipulation both in solution and in the solid state have been the main limitation toward the extensive use of such tubular carbon frameworks. Therefore, to take advantage of the remarkable physical properties of such carbon species, the nanotubes have been functionalized with organic pendant groups, which can enhance both the solubility in organic solvents and the number of reactive sites for further covalent integration into multicomponent organic materials. 9-11 The main chemical approaches for the modification of such carbon structures can be grouped into two categories: (i) covalent and (ii) noncovalent functionalization. The covalent derivatization of SWNTs has been mainly focused to modify the sidewalls using oxidizing acids, 12,13 fluorine, 14,15 alkyl- lithium and Grignard reagents, aryl diazonium salts, 16 azomethine ylides, 17 nitrenes, 18 and organic radicals. 19 These products of functionalization, however, are difficult to characterize with classical analytical techniques such as those used in standard organic chemistry. The most popular techniques are scanning and transmission electron micros- copy (SEM and TEM), atomic force microscopy (AFM), thermogravimetric analysis (TGA), and Raman and near- infrared (NIR) spectroscopies. Raman spectroscopy is com- monly used as an analytical method to determine the extent of sidewall functionalization by following the occurrence and magnitude of the D mode at 1330 cm -1 . However, the distribution of the addend groups along the tube has not been detected yet. Despite the importance as imaging techniques, TEM and SEM are not capable of evaluating the covalent modification of SWNTs because the image does not visualize the presence of organic pendant groups. The TGA technique is capable of measuring the amount of organic material in the sample but does not provide an unambiguous separation between the presence of covalent or noncovalent attached organic species. With these problems in mind, a few authors have started to employ other characterization techniques, such as scanning tunneling microscopy (STM) to directly image the organic modification introduced on the SWNTs. 20,21 Specifically, the first STM study of fluorinated SWNTs * To whom correspondence should be addressed. E-mail: prato@units.it (M.P.); modesti@tasc.infm.it (S.M.); Moreno.Meneghetti@unipd.it (M.M.). ² Dipartimento di Scienze Farmaceutiche and INSTM UdR Trieste, Universita ` degli Studi di Trieste. ‡ Laboratorio Nazionale TASC dell’ INFM. § Dipartimento di Fisica, Universita ` di Trieste. | Dipartimento di Scienze Chimiche, Universita ` degli Studi di Padova. NANO LETTERS 2006 Vol. 6, No. 7 1408-1414 10.1021/nl060394d CCC: $33.50 © 2006 American Chemical Society Published on Web 06/24/2006 Downloaded by SINCROTRONE TRIESTE on September 19, 2009 | http://pubs.acs.org Publication Date (Web): June 24, 2006 | doi: 10.1021/nl060394d