Visualizing ultrafast exciton dynamics in carbon nanotubes by nano-infrared spectroscopy

Carbon nanotubes (CNTs) are nanometer-scale wires that behave either like metals or semiconductors depending on the atomic arrangement. Their unique electrical and optical properties make them promising materials for next-generation nanoelectronics and nanophotonics. In contrast to conventional semiconductors like silicon, optical processes in CNTs are largely governed by excitons, bound pairs of electrons and holes. Understanding exciton dynamics is thus crucial for the design of CNT-based devices. However, it has been a significant challenge to visualize such dynamics at extreme spatial (~100 nm) and temporal (down to sub-picosecond) scales, which are intrinsic to ultrathin materials like CNTs. To address this, the research team employed an advanced ultrafast infrared near-field optical microscope, which delivered femtosecond infrared pulses into nanoscale regions by focusing light onto a sharp metallic tip. Using this system, the team revealed that exciton relaxation dynamics in individual CNTs is highly sensitive to structural disorder and interactions with neighboring CNTs or underlying substrates. These findings underscore the critical role of local environments in controlling exciton behavior in nanodevices. The researchers further develop a theoretical model that reproduces the experimental results, offering a foundation for understanding the interaction between infrared near fields and matter, including other nanomaterials. This study successfully demonstrates the potential of nano-infrared near-field microscopy to visualize ultrafast quantum processes at the nanoscale, paving the way for the development of high-speed nanoscale photonics devices based on nanocarbon materials.

(Credit: Takashi Kumagai, Restriction: CC BY)

Papers

Journal: Science Advances

Title: Ultrafast infrared nano-imaging of local electron-hole dynamics in CVD-grown single-walled carbon nanotubes

Authors: Jun Nishida*, Keigo Otsuka, Taketoshi Minato, Yuichiro K. Kato, Takashi Kumagai*

DOI: 10.1126/sciadv.adv9584