In situ raman spectroelectrochemistry of single-walled carbon nanotubes: Investigation of materials enriched with (6,5) tubes

Single-walled carbon nanotubes (CoMoCat) have been enriched with (6,5) tubes via density-gradient ultracentrifugation. Thin solid films of quasi-isolated nanotubes were fabricated from a solution of sorted nanotubes by vacuum filtration and extraction with water. Optical spectroscopy in the vis-NIR region and Raman spectroscopy were used to characterize these materials. The experimental studies were supported by a theoretical analysis of the electronic and vibrational structure of selected (n, m) tubes by using density functional theory. Besides the most abundant tubes (6,5), the experimental and theoretical data for tubes (6,4),(7,3),(7,5),(8,3), and (9,1) are also discussed. A detailed investigation by in situ Raman spectroelectrochemistry was focused on the effects of electrochemical p-/n-doping. The experimental analysis of the intensities and frequencies of the radial breathing mode and the tangential displacement modes were correlated with the theoretically calculated optical transition energies and Raman frequencies. It was demonstrated that electrochemical charging is a useful tool for the study of doping effects on the electronic structure of carbon nanotubes.