Physica B 323 (2002) 259–261 Stoichiometry dependence of the Raman spectrum of Li-doped single-wall carbon nanotubes N. Bendiab a , E. Anglaret a, *, J.-L. Bantignies a , J.L. Sauvajol a , P. Petit b , C. Mathis b a GDPC, UMR CNRS 5581, Universit ! e Montpellier II, CC 26, 34095 Montpellier Cedex 5, France b Institut Charles Sadron, 67000 Strasbourg, France Abstract We study the Raman spectra of Li-doped SWNT films. A monotonic upshift of the tangential modes, and a concomitant progressive loss of the resonant behavior of the Raman signal, are evidenced when the Li rate increases. No significant change is observed all over the temperature range 10–300 K. r 2002 Elsevier Science B.V. All rights reserved. PACS: 78.30.Na; 61.48.+c Keywords: Nanotubes; Raman scattering 1. Introduction Because of their specific structure, bundles of SWNT are interesting intercalation hosts, which can form intercalated synthetic metals by alkali- metals doping [1–9]. To study properly the proper- ties of SWNT under doping, the control of the stoichiometry is crucial. Recently, it was demon- strated that the precise chemical composition of doped SWNT could be obtained by performing redox reactions between SWNT thin films and solutions of organic radical-anions [2,3]. Raman scattering for SWNT is a resonant process associated with allowed optical transitions between spikes in the 1D electronic density of states of metallic or semiconducting tubes which fall in the visible and near-infrared ranges [4]. Fig. 1a displays the results for a SWNT sample with a mean-tube diameter of 1.4 nm. A broad and asymmetric band around 1540 cm À1 and a sharp peak at 1580 cm À1 are measured for an excitation energy of 1.92 eV while a series of symmetric lines with a dominant peak around 1590 cm À1 is obser- ved for an excitation energy of 2.41 eV. These results are assigned to resonance on metallic (semiconduct- ing) tubes at 1.92 eV (2.41 eV) [4–6]. Because vibration features are sensitive to both the intercala- tion and charge transfer, Raman studies allow investigating the evolution of the structural and electronic properties of SWNT under doping. In this communication, we report a Raman investigation performed on thin films of Li-doped SWNTs (Li x C) of different controlled stoichiometries. 2. Materials and experiments Thin films of SWNT were obtained by disper- sing colarettes prepared by the arc electric method *Corresponding author. Fax: +33-4-67-14-4637. E-mail address: eric@gdpc.univ-montp2.fr (E. Anglaret). 0921-4526/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII:S0921-4526(02)00983-3