The origin of nondispersive Raman lines in the D-band region for ferrocene@HiPco SWCNTs transformed at high temperatures

Abstract

Small diameter single-walled carbon nanotubes can be filled with carbon-rich molecules if the latter are small enough. For HiPco tubes ferrocene turned out to be appropriate. After filling and high temperature treatment (transformation) new Raman lines are observed. Here we show that these lines appear also for small diameter DIPS tubes after similar temperature treatment and that all new lines originate from one special molecule. This molecule has a C=C stretch vibration at 1597 cm observed on top of the G-line components of the tubes. Mass spectra from the transformed tube material revealed compounds with masses of the order of 500–750 Da which are typical for large organic molecules. Experiments with isotope labeled ferrocene showed characteristic changes of the Raman response which extend beyond the consequences of a simple change of atomic masses. DFT calculations using B3LYP functionals revealed that narrow width and short length carbon nanoribbons such as quaterrylene or dimeric PTCDA are possible candidates for the new molecules.