increases the intensity of the D peak due to formation of aryl-nanotube bond and decreases the tangential mode due loss of electronic resonance. These two effects are generally summed together as increase in their peaks ratio (D/G). RBM peaks of metallic nanotubes decay and the peaks corresponding to those of semiconducting nanotubes remain almost unchanged. Reaction mechanism Diazonium reagent and SWNT reaction has a two step mechanism. First, the diazonium reagent adsorbs noncovalently to an empty site on the nanotube surface, forming a charge-transfer complex. This is a fast, selective noncovalent adsorption and diazonium group in this complex partially dopes the nanotube, diminishing the tangential mode in the Raman spectrum. Desorption of A from nanotube is negligible (k−1 ~ 0). In second step complex B then decomposes to form a covalent bond with the nanotube surface. This is a slower step that need not be selective and is represented by the restoration of the G peak and increase in the D band. Reversibility of diazonium chemistry Nanotubes reacted with the diazonium reagent can be converted back into pristine nanotubes when thermally treated at 300 °C in an atmosphere of inert gas. This cleaves the aryl hydroxyl moieties from the nanotube sidewall and restores the spectroscopic feature (Raman and absorption spectra) of pristine nanotube. Chemical separation of metallic and semiconducting SWNTs Metallic and semiconducting carbon nanotubes generally coexist in as-grown materials. To get only semiconducting or only metallic nanotubes selective functionalization of metallic SWNTs via 4-hydroxybenzene diazonium can be used. Separation can be done in solution by deprotonation of the p-hydroxybenzene group on the reacted nanotubes (metallic) in alkaline solution followed by electrophoretic separation of these charged species from the neutral species (semiconducting nanotubes). This followed by annealing would give separated pristine semiconducting and metallic SWNT. References Carbon nanotubes