Résumé
The unique optical properties of single-wall carbon nanotubes (SWNTs) are very promising for the development of novel opto-electronic components and sensors with applications in many fields. Despite numerous studies performed using photoluminescence or Raman and Rayleigh scattering, knowledge of their optical response is still partial, in particular direct and quantitative access to the intrinsic absorption characteristics of SWNT is still challenging. Their precise investigation is made difficult by the large heterogeneities of the carbon nanotube structural parameters in most synthesized ensembles, leading to measurement of mean properties. This can be avoided by performing optical investigations on individual nanotubes. We show here that the spatial modulation spectroscopy (SMS) technique, initially developed to quantitatively study the optical response of single metal nanoparticles 1 , can be applied to the investigation of individual SWNTs 2,3 . As compared to other optical techniques, SMS has the key advantage of being sensitive to the nano-object absorption and to directly measure its absolute absorption cross-section. Using this approach, we have determined, over a broad optical spectral range, the absorption spectrum of semiconducting individual SWNTs and the oscillator strength of their different excitonic resonances. A non-resonant background is also identified and its cross-section comparable to the ideal graphene optical absorbance. Furthermore, investigation of the same SWNT either free-standing or lying on a substrate shows large broadening of the excitonic resonances, as well as strong weakening of polarization-dependent antenna effects, due to SWNT-substrate interaction. [1] A.Arbouet, D.Christofilos, N.Del Fatti and F.Vallée ; J-R.Huntzinger, L.Arnaud, P.Billaud and M. Broyer, Physical Review Letters 93, 127401 (2004). [2] D.Christofilos , J-C.Blancon , J.Arvanitidis, A.San Miguel, A.Ayari, N.Del Fatti and F.Vallée, Journal of Physical Chemistry Letters 3, 1176 (2012). [3] J.-C. Blancon, M. Paillet, H.N.Tran, X.T.Than, S. Aberra-Guebrou, A. Ayari, A. San Miguel, N-M. Phan, A-A. Zahab, J-L. Sauvajol, N. Del Fatti and F. Vallée, Nature Communications 4:2542 doi:10.1038/ncomms3542 (2013).