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O: Fachverband Oberflächenphysik

O 116: Focus Session: Structural Dynamics in Nanoscale Materials, Probed by Ultrafast Electron Pulses III

O 116.1: Hauptvortrag

Freitag, 16. März 2018, 10:30–11:00, HE 101

Imaging Coherent, Nanoscale Acoustic-Phonon Dynamics with Ultrafast Electron Microscopy — •David Flannigan, Daniel Cremons, Daniel Du, Dayne Plemmons, and Spencer Reisbick — University of Minnesota, Dept. of Chemical Engineering and Materials Science, Minneapolis, MN, USA

Here, I will describe our work on the development and the application of ultrafast electron microscopy [1]. I will begin with a brief overview of the UEM technology specific to our lab, focusing on imaging and operating at low instrument repetition rates. Following this, I will describe our progress in resolving the influence of nanoscale structural discontinuities on coherent, elastic strain-wave dynamics in a variety of materials [2-4]. For example, in transition-metal dichalcogenides, we find that wave trains emerge at extended discontinuities and that preferred propagation directions are independent of crystallographic orientation. In Ge, we find that individual phonon wave fronts propagate at hypersonic velocities and display a picosecond phase-velocity dispersion to the speed of sound. Overall, the observed dynamics indicate a single Lamb-type mode is excited several tens of picoseconds after femtosecond photoexcitation, suggestive of a link to charge-carrier dynamics via Auger recombination and the launch of electron-hole plasma waves.

[1] D. A. Plemmons and D. J. Flannigan, Chem. Phys. Lett. 683, 186 (2017). [2] D. R. Cremons, D. A. Plemmons, and D. J. Flannigan, Nat. Commun. 7, 11230 (2016). [3] D. R. Cremons, D. A. Plemmons, and D. J. Flannigan, Struct. Dyn. 4, 044019 (2017). [4] D. R. Cremons, D. X. Du, and D. J. Flannigan, Phys. Rev. Materials 1, 073801 (2017).