Supplementary Material for “Fano Resonances in Mid-Infrared Spectra of Single-Walled Carbon Nanotubes” Fran¸ cois Lapointe, ´ Etienne Gaufr` es, Isabelle Tremblay, Nathalie Y-Wa Tang, and Richard Martel * D´ epartement de chimie, Universit´ e de Montr´ eal, C. P. 6128, Succursale Centre-Ville, Montr´ eal, Qu´ ebec H2C 3J7, Canada and Regroupement Qu´ eb´ ecois sur les Mat´ eriaux de Pointe (RQMP) Patrick Desjardins D´ epartement de g´ enie physique, ´ Ecole Polytechnique de Montr´ eal, Montr´ eal, C. P. 6079, Succursale Centre-ville, Montr´ eal, Qu´ ebec H3C 3A7, Canada and Regroupement Qu´ eb´ ecois sur les Mat´ eriaux de Pointe (RQMP) This work revisits the physics giving rise to the carbon nanotubes phonon bands in the mid- infrared. Our measurements of doped and undoped samples of single-walled carbon nanotubes in Fourier transform infrared spectroscopy show that the phonon bands exhibit an asymmetric lineshape and that their effective cross-section is enhanced upon doping. We relate these observations to electron-phonon coupling or, more specifically, to a Fano resonance phenomenon. We note that only dopant-induced intra-band transitions couple to the phonon modes and that defects induced in the sidewall increase the resonance probabilities. METHODOLOGY Purification and suspension Laser ablation single-walled carbon nanotubes (SWNTs) (Benoit Simard, NRC Steacie Institute, Ottawa) were purified using a process described else- where [1]. Briefly, 100 mg of SWNTs were refluxed in concentrated nitric acid (70%, Certified ACS Plus, Fisher Scientific) for four hours, and filtrated over a PTFE membrane (pore size 1.2 μm, Sartorius Stadim Biotech). The SWNTs were then dispersed in deionized water (Millipore Milli-Q, 18.2 MΩ), refluxed overnight, and filtrated again over a PTFE membrane. The resulting SWNTs were dispersed in a 1% w/V sodium cholate solution (from ox or sheep bile, ≥99%, Sigma-Aldrich) in deionized water. The dispersion was submitted to ultrasonification for 30 min. in a bath (VWR Model 75D) and 30 min. using a high power microtip (Branson Sonifier 450, 400 watt, duty cy- cle 50%, output 3). Afterward, we used ultracentrifuga- tion (20,800 rpm, one hour, 100,000 g, Beckman L8-70, rotor SW 41 Ti) to remove bundles and denser material from the dispersion. The supernatant was kept and the suspension was found to be stable over months. Films Films of SWNTs were made using a procedure devel- oped by Wu et al. [2] Three milliliters of the suspension were filtrated over mixed cellulose ester / cellulose nitrate filters (0.22 μm, Millipore GSTF-047-00). The films can be transferred to a convenient substrate by dissolving the filter in acetone (Certified ACS, Fisher Scientific) for 30 min. Annealing Further cleaning and de-doping of the SWNT films was performed by annealing in a vacuum quartz tube furnace at 1100 K. The quality of the vacuum was maintained be- tween 2 ×10 -5 and 2 ×10 -6 mbar using a turbomolecular pump. The spectra of the intrinsic state of the SWNTs films were taken right after annealing because it is known that the oxygen / water redox couple is a p type dopant for SWNTs [3]. Doping Three different oxidizers were chosen for dop- ing SWNT. 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ, 98%, Sigma-Aldrich) and iron(III) chloride hex- ahydrate (FeCl 3 · 6H 2 O, ≥98%, Sigma-Aldrich) solutions were made at a concentration of 25 mM in acetonitrile (reagent grade, American Chemicals Ltd). Thionyl chlo- ride (SOCl 2 , 99+%, American Chemicals Ltd) was used in pure form. The SWNTs films were left in the dopant for two days, rinsed in acetonitrile, dried with a N 2 stream, and the spectra were performed shortly after their removal from solution. Bromophenyl Functionalization A solution at a concentration of 0.79 mM of 4- bromobenzenediazonium tetrafluoroborate (96%, Sigma- Aldrich) was prepared with degassed deionized water (Millipore Milli-Q, 18.2 MΩ) and the pH was adjusted to ∼ 10 with NaOH [4]. The SWNT film was dipped into the aqueous salt solution for 10 minutes, rinsed with water, then with 2-propanol (Certified ACS Plus, Fisher