Time-of-Flight Secondary Ion Mass Spectroscopy Characterization of the Covalent Bonding between a Carbon Surface and Aryl Groups Catherine Combellas,* ,† Fre ´de ´ric Kanoufi, † Jean Pinson, ‡ and Fetah I. Podvorica § Laboratoire Environnement et Chimie Analytique, CNRS-ESPCI, 10 rue Vauquelin, 75231 Paris Cedex 05, France, Alchimer, Z. I. de la Bonde, 15 rue du Buisson aux Fraises, 91300 Massy, France, and Chemistry Department of Natural Sciences Faculty, University of Prishtina, rr. “Ne ¨ na Tereze” nr. 5, Prishtina, Kosovo Received July 27, 2004. In Final Form: September 10, 2004 Grafting of aryl layers derived from aryl diazonium salts onto glassy carbon electrodes is observed by time-of-flight secondary ion mass spectroscopy (ToF-SIMS). The grafting occurs spontaneously when a glassy carbon plate is immersed into a solution of aryl diazonium salt and can be enhanced by biasing the carbon plate at a potential a little more negative than the diazonium salt reduction. C-C and C-O covalent bonding are believed to be responsible for the strong attachment of these layers onto the carbon substrate. Fragments containing aryl dimers, trimers, or tetramers are also observed. A mechanism is proposed to account for the formation of these polymeric chains. 1. Introduction Electrochemical reduction of aryl diazonium salts at a carbon electrode leads to the covalent bonding of the aryl group to the carbon surface according to 1-23 In step I, the carbon electrode is biased at about 0 V/SCE (saturated calomel electrode) and an aryl radical is obtained directly, since the electron transfer to the diazonium cation is concerted with C-N bond cleavage. 4 In step II, the aryl radicals are linked to the carbon surface. The reaction can be performed in an aprotic medium such as acetonitrile as well as in acidic water. 2 Organic layers obtained with diverse diazonium salts have been characterized by different methods such as cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), 1-3,8 vibrational spectroscopy (polarization modulation infrared reflection absorption spectroscopy (PMIRRAS)), 2 Raman spectroscopy, 5-7 and Rutherford backscattering (RBS). 2 In the case of glassy carbon (GC), the influence of such grafted organic layers on electron transfer rates has been measured. 8 Layers grafted on highly oriented pyrolytic graphite (HOPG) have been observed by atomic force 9,10 and scanning tunneling microscopies. 11 These modified surfaces have been used for different applications, among which we can mention the linking of enzymes such as glucose oxidase 12 or avidine-biotine, 13 the bonding of gold nanoparticles, 14 the limitation of protein adsorption, 15 and the functionalization of poly(tetrafluoroethylene) (PTFE) after carbonization. 16 Compact layers of aryl groups can also be grafted on surfaces by the electrochemical reduction of diazonium salts on hydrogenated Si(111) 17-19 or on metals. 20-23 Grafting of aryl groups derived from diazonium salts has also been obtained directly without electrochemical activation on carbon black to yield materials for the plastics, rubber, and textile industries 24 and also, more recently, on semiconductors and palladium. 25 Although the presence of an organic layer on top of conductive surfaces (carbon, semiconductor, or metal) has * To whom correspondence should be addressed. 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