title: Ultrafast Three-Dimensional X-ray Imaging of Deformation Modes in ZnO Nanocrystals.
abstract: Imaging the dynamical response of materials following ultrafast excitation can reveal energy transduction mechanisms and their dissipation pathways, as well as material stability under conditions far from equilibrium. Such dynamical behavior is challenging to characterize, especially operando at nanoscopic spatiotemporal scales. In this letter, we use X-ray coherent diffractive imaging to show that ultrafast laser excitation of a ZnO nanocrystal induces a rich set of deformation dynamics including characteristic "hard" or inhomogeneous and "soft" or homogeneous modes at different time scales, corresponding respectively to the propagation of acoustic phonons and resonant oscillation of the crystal. By integrating the 3D nanocrystal structure obtained from the ultrafast X-ray measurements with a continuum thermo-electro-mechanical finite element model, we elucidate the deformation mechanisms following laser excitation, in particular, a torsional mode that generates a 50% greater electric potential gradient than that resulting from the flexural mode. Understanding of the time-dependence of these mechanisms on ultrafast scales has significant implications for development of new materials for nanoscale power generation.
authors.affiliation: Advanced Photon Source, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Mathew J
authors.initials: MJ
authors.lastname: Cherukara
authors.affiliation: Center for Nanoscale Materials, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Kiran
authors.initials: K
authors.lastname: Sasikumar
authors.affiliation: Advanced Photon Source, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Wonsuk
authors.initials: W
authors.lastname: Cha
authors.affiliation: Center for Nanoscale Materials, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Badri
authors.initials: B
authors.lastname: Narayanan
authors.affiliation: ESRF - The European Synchrotron , 71 Avenue des Martyrs, Grenoble 38000 , France.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Leake
authors.affiliation: Advanced Photon Source, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Eric M
authors.initials: EM
authors.lastname: Dufresne
authors.affiliation: Mathematics and Computer Science, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Tom
authors.initials: T
authors.lastname: Peterka
authors.affiliation: Center for Nanoscale Materials, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Ian
authors.initials: I
authors.lastname: McNulty
authors.affiliation: Advanced Photon Source, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Haidan
authors.initials: H
authors.lastname: Wen
authors.affiliation: Center for Nanoscale Materials, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Subramanian K R S
authors.identifier: 0000-0002-9708-396X
authors.initials: SK
authors.lastname: Sankaranarayanan
authors.affiliation: Advanced Photon Source, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Ross J
authors.initials: RJ
authors.lastname: Harder
mesh_terms: D003460:Crystallization; D021621:Imaging, Three-Dimensional; D007700:Kinetics; D007834:Lasers; D008422:Materials Testing; D053758:Nanoparticles / Q000737:chemistry*; D060739:Phonons; D055585:Physical Phenomena; D014965:X-Rays; D015034:Zinc Oxide / Q000737:chemistry*
chemical_list: D015034:Zinc Oxide
keywords: ZnO, nanocrystal; integrated imaging; power generation; ultrafast X-ray