Structural and electronic distortions in individual carbon nanotubes under laser irradiation in the electron microscope

Abstract

Correlated electronic and structural distortions in individual carbon nanotubes induced by photon excitation are observed for the first time by using a unique in situ transmission electron microscope configuration. By combining sub-100-meV resolution electron energy-loss spectroscopy with in situ photon excitation of the specimen, we are able to measure carbon nanotube expansions coupled to electronic transitions in their density of states as a direct consequence of the photon excitation/irradiation. Laser-induced effects are recorded in electron energy-loss spectra, which show reversible changes in the carbon unoccupied conduction band with 2$p$ character, as well as in the carbon plasmon spectral band, for both individual single-wall and individual multiwall carbon nanotubes. Furthermore, for single-walled carbon nanotubes, we see significant changes in the density of states close to the Fermi energy. The observed changes are discussed in the context of increased interatomic spacing, resulting from photon-induced thermal expansion and exciton screening enhancement due to photocarriers. These are the first measurements of photon-induced correlated structural and electronic changes at the atomic level in any nanoscale material. This new capability and technique should enable a new understanding of photon-induced structural, chemical, and electronic reactions across a range of nanoscale systems.