ELSEVIER Synthetic Metals 101 (1999) 184-187 Studies by SERS spectroscopy of the structural properties of conducting polymers and carbon nanotubes S. Lefrant”, I. Balto$, M. Lamy de la Chapelle4”, M. Baibaracb, G. Louam’, C. Journetd, P. Bcmierd a Laboratoire de Physique Cristalline, IMN, Universitd de Nantes, France b National Institute of Materials Physics, Bucharest, Romania ’ Trinity College, Dublin, ireland ’ Groupe de Dynamique des Phases condenskes, Universitd Montpellier 2, Montpellier, France Abstract After being dispersed in liquid solvents (Ethanol, CHCl,), conducting polymers and singlewalled nanotubes have been deposited on ruguous substrats (Au, Ag, Cu). With FT Raman technique (laser excitation : 1064 nm), we have obtained SERS signal of both conductiong polymers and singlewalled nanotubes. The Raman signals change with substrat and/or solvent, which could be correlated with the size of clusters formed at the surface and then to the deposition mechanism. The main advantage of the >SERS technique will be emphasized in terms of enhancement as a powerful technique to study nanoparticles. Keywords: conducting polymers, carbon nanotubes, Raman spectroscopy. 1. Introduction The Surface Enhanced Raman Scattering (SERS) has lately proved to be a very useful technique for providing high-quality spectra and allows observation of fine structural details of films with very small thickness [l-3]. Even though many details of the process have yet to be understood, it is generally admitted that exaltation has a double origin: an electromagnetic one and a chemical one. Further informations on this technique can be provided in the ref. 141. The present work is a synthesis of our research on the SERS spectroscopy of carbonaceous materials : poly(3-hexyl thiophene) (3-PHT), glassy carbon and singlewalled nanotubes (SWNT’s). Special attention has been given now to the dependence of the SERS spectra on the roughness characteristics of the metal support, by analogy with the use of a diffraction grating as an optical coupler. This paper also reports results on the SERS spectroscopy of nanometric structures, particularly the SERS spectra of the carbon nanotubes. 2. Samples preparation The substrat : The strong dependence of SERS spectra intensity on metal support roughness [4,5] imposes some restrictions on the technique of preparation of the metal films. We used the vacuum evaporation technique with a deposition rate of 1 nm/sec at a pressure lower than 10“ torr, with the atomic beam at almost grazing incidence (q,=SO’) on the microscope slide used as a target support [lo]. The decrease of the incidence angle s of the atomic beam modifies the roughness of the metallic film which in turn determines an important decrease of the intensity of the SERS spectra. By controlling the evaporation geometry and the quantity of evaporated metal, we ensured a good reproducibility of the thickness and roughness of the metal films used as supports in our SERS experiments. The Raman active metallic films prepared by means of the above technique were inspected by scanning electron microscopy. A typical aspect of a rough gold surface with a good Raman activity is presented in Fig.1. Fig 1 : Scanning electronic microscopy image of the rough gold surface To avoid the disturbing photoluminescence background appearing when a visible excitation is used, the SERS studies reported in this paper were carried out under 1064 nm iaser excitation. The spectra were recorded in a back scattering 0379-677919915 - see front matter 0 1999 Elsevier Science S.A. All rights reserved. PII: SO379-6779(98)00307-5