Complete structural characterization of single carbon nanotubes by Rayleigh scattering circular dichroism

Non-invasive, high-throughput spectroscopic techniques can identify chiral indices (n,m) of carbon nanotubes down to the single-tube level(1-6). Yet, for complete characterization and to unlock full functionality, the handedness, the structural property associated with mirror symmetry breaking, also needs to be identified accurately and efficiently(7-14). So far, optical methods fail in the handedness characterization of single nanotubes because of the extremely weak chiroptical signals (roughly 10(-7)) compared with the excitation light(15,16). Here we demonstrate the complete structure identification of single nanotubes in terms of both chiral indices and handedness by Rayleigh scattering circular dichroism. Our method is based on the background-free feature of Rayleigh scattering collected at an oblique angle, which enhances the nanotube's chiroptical signal by three to four orders of magnitude compared with conventional absorption circular dichroism. We measured a total of 30 single-walled carbon nanotubes including both semiconducting and metallic nanotubes and found that their absolute chiroptical signals show a distinct structure dependence, which can be qualitatively understood through tight-binding calculations. Our strategy enables the exploration of handedness-related functionality of single nanotubes and provides a facile platform for chiral discrimination and chiral device exploration at the level of individual nanomaterials.

Automated summary

Non-invasive, high-throughput spectroscopic techniques can identify the chiral indices of carbon nanotubes down to the single-tube level. However, optical methods have failed to accurately characterize the handedness of single nanotubes due to weak chiroptical signals. By using Rayleigh scattering circular dichroism, the complete structure identification of single nanotubes in terms of both chiral indices and handedness has been successfully demonstrated. This method enhances the nanotube's chiroptical signal significantly, enabling exploration of handedness-related functionality of single nanotubes.