The vibrational and electronic properties of Br 2 -adsorbed double-wall carbon nanotubes ͑DWNTs͒ were investigated by resonance Raman scattering. Special attention was given to distinguish the behavior between S/M and M/S outer/inner semiconducting ͑S͒ and metallic ͑M͒ tubes. By using three laser excitation energies 2.33, 1.96, and 1.58 eV, resonance Raman spectra were obtained for the DWNTs before and after bromine adsorption, and also for the Br-Br molecular resonance, thereby facilitating the study of charge transfer between the DWNTs and the bromine. It was found that Br 2 molecules act as acceptors and that metallic nanotubes are specially sensitive to the presence of Br 2 molecules even when they constitute the inner tubes of DWNTs.

This report focuses on the effects of different Br2 doping levels on the radial breathing modes of "double-wall carbon nanotube (DWNT) buckypaper". The resonance Raman profile of the Br2 bands are shown for different DWNT configurations with different Br2 doping levels. Near the maximum intensity of the resonance Raman profile, mainly the Br2 molecules adsorbed on the DWNT surface contribute strongly to the observed omega(Br-Br) Raman signal.

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