Optical Characterization of Double-Wall Carbon Nanotubes: Evidence for Inner Tube Shielding

This paper presents a comprehensive optical study of double-wall carbon nanotubes (DWNTs) grown by chemical vapor deposition, using optical absorption, photoluminescence (PL), and Raman spectroscopies. Extending the spectral ranges of absorption and PL measurements beyond 2300 nm made it possible to detect signals both from the inner and the outer shells of DWNTs. Application of in situ perturbations, namely, oxidation with light-generated ozone and electrochemical doping, unambiguously proved the double-wall structure of our samples and revealed the efficient shielding of the inner DWNT shells by the outer shells. Analysis of the absorption spectra measured under progressive ozone oxidation allowed us to decompose the total DWNT absorption into the contributions from the inner and outer shells and to estimate the filling ratio of DWNTs.