Raman spectroscopy uses visible light to acquire vibrational fingerprints of molecules, thus making it a powerful tool for chemical analysis in a wide range of media. Its potential for optical imaging at high resolution is, however, severely limited by the fact that the Raman effect is weak. Here, we report the discovery of a giant Raman scattering effect from encapsulated and aggregated dye molecules inside single-walled carbon nanotubes (SWNTs). Measurements performed on rod-like dyes, such as α-sexithiophene and βcarotene, assembled inside SWNTs as highly polarizable J-aggregates indicate a resonant Raman cross-section (CS) of ~10-21 cm 2 /sr, which is well above the CS required for detecting individual aggregates at the highest optical resolution. Free from fluorescence background and photobleaching, this giant Raman effect allows the realization of a library of functionalized and biocompatible nanoprobe labels for Raman imaging with robust detection using multispectral analysis.

Covalent functionalization of single-wall carbon nanotubes (SWNTs) is currently developing as one of the most powerful tools enabling their processing, manipulation, and assembly from solution. 1 SWNTs are rather inert, and only harsh chemical or mechanical treatments can activate the highly conjugated C-C bonds. Moreover, the functionalization introduces disorder that disrupts the electrical and optical properties of SWNTs. Thus, the covalent SWNT chemistry presents important issues, and more sensitive methods are required in order to gain a better understanding of the reactions. For example, oxidation processes involving hard sonication and strong acids were among the first approaches to functionalize the SWNT sidewalls, 2 but they are known to introduce irreversible damage. 1b,3 Recently, new functionalization reactions using radical addition, such as the diazonium, fluorination, and peroxide reactions, have been developed in order to avoid permanent damage. The diazonium reaction, for instance, provides an effective path to anchor new groups onto the sidewalls, 4 and a large variety of functionalities can then be attached. 5 This approach is particularly interesting because it is general. Raman studies have also shown evidence that the reaction is reversible. However, the Raman signature is difficult to interpret due to stringent selection rules and complications associated with resonance enhancement process. 6 Here we present a general and sensitive method to probe the reversibility of SWNT sidewall reactions. The approach is to combine Raman spectroscopy and conductance measurements from a large ensemble of nanotube field-effect transistors (SWNT FET). The data are taken during several functionalization/ defunctionalization cycles and then used to build a good statistic on the evolution of the reactions. We present here the case of the diazonium reaction. The study reveals for the first time that the reaction is partially reversible and leads to a small accumulation of defects onto the SWNT sidewall. The reaction rate is also much faster for the metallic SWNT species.We fully characterized 22 p-type SWNT FETs during several cycles of functionalization (f-SWNT) and defunctionalization (d-SWNT) reactions. The SWNT FETs are about 0.5 µm long and consist of 1-3 bundles of 1.5-5 nm of height, as determined by AFM imaging. We functionalized the SWNT FETs using a solventfree diazotization and coupling procedure. 7 The defunctionalization was conducted by annealing the devices at 500°C for 1 h under vacuum (4 × 10 -5 mbar). A TGA and a thermodesorption analysis confirm that these conditions ensure a complete defunctionalization. A typical desorption spectra is shown in Figure 2 with three main peaks at 100, 330, and 430°C. The first is simply water desorption, while the peaks at 330-410°C are associated with the removal of the iodophenyl from the sidewall of the SWNTs. No other desorption was observed at a temperature up to 650°C.Typical transfer characteristics of SWNT devices taken before and after reactions are ...

Double-walled carbon nanotubes (DWNTs) present an original coaxial geometry in which the inner wall is naturally protected from the environment by the outer wall. Covalent functionalization is introduced here as an effective approach to investigate DWNT devices. Performed using an aryldiazonium salt, the functionalization is reversible upon thermal annealing and occurs strictly at the surface of the outer wall, leaving the inner wall essentially unaltered by the chemical bonding. Measurements on functionalized DWNT transistors show that the electrical current is carried by the inner wall and provide unambiguous identification of the metallic or semiconducting character of both walls. New insights about current saturation at high bias in DWNTs are also presented as an illustration of new experiments unlocked by the method. The wall-selectivity of the functionalization not only enables selective optical and electrical probing of the DWNTs, but it also paves the way to designing novel electronic devices in which the inner wall is used for electrical transport while the outer wall chemically interacts with the environment.