In-situ vis-near-infrared and Raman spectroelectrochemistry of double-walled carbon naotubes

Double-walled carbon nanotubes (DWCNTs) are studied using in-situ visible-near-infrared (vis-NIR) and in-situ Raman spectroelectrochemistry. Electrochemical vis-NIR spectroscopy reveals a complex picture of DWCNTs due to the overlap of the features of the inner and outer tubes and possible optical transitions, which are not predicted by the simple tight-binding model. The optical transitions are bleached upon electrochemical doping. This is qualitatively understood to be a consequence of the Fermi-level shift by the applied potential relative to the van Hove singularity. In-situ Raman spectra are quenched by the applied cathodic/anodic potentials due to the loss of resonance by electrochemical charging. The electrochemical tuning of Raman spectra proceeds distinctly for inner and outer tubes. While the bands of outer tubes rapidly follow the potential change, the features of inner tubes respond relatively slowly to electrochemical perturbations. The Raman D-modc of DWCNTs was found to be bifurcated upon electrochemical charging, which is similar to the behavior of the tangential displacement mode. Ionic liquids are good electrolytes for the spectroelectrochemistry of DWCNTs, even at extreme applied potentials. They allow the deconvolution of the tangential modes of the inner and outer tubes at both cathodic and anodic doping.