title: 4D electron microscopy visualization of anisotropic atomic motions in carbon nanotubes.
abstract: We report the anisotropic atomic expansion dynamics of multi-walled carbon nanotubes, using 4D electron microscopy. From time-resolved diffraction on the picosecond to millisecond scale, following ultrafast heating at the rate of 10(13) K/s, it is shown that nanotubes expand only in the radial (intertubule) direction, whereas no significant change is observed in the intratubular axial or equatorial dimensions. The non-equilibrium heating occurs on an ultrafast time scale, indicating that the anisotropy is the result of an efficient electron-lattice coupling and is maintained up to equilibration. The recovery time, which measures the heat dissipation rate for equilibration, was found to be on the order of ∼100 μs. This recovery is reproduced theoretically by considering the composite specimen-substrate heat exchange.
authors.affiliation: Physical Biology Center for Ultrafast Science and Technology, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, 91125, United States.
authors.forename: Sang Tae
authors.initials: ST
authors.lastname: Park
authors.forename: David J
authors.initials: DJ
authors.lastname: Flannigan
authors.forename: Ahmed H
authors.initials: AH
authors.lastname: Zewail