Influence of Discrete Defects on Observed Acoustic-Phonon Dynamics in Layered Materials Probed with Ultrafast Electron Microscopy

Spencer Reisbick, Yichao Zhang, David J. Flannigan

Research output: Contribution to journalArticlepeer-review

13 Scopus citations


The structural anisotropy of layered materials leads to disparate lattice responses along different crystallographic directions following femtosecond photoexcitation. Ultrafast scattering methods are well-suited to resolving such responses, though probe size and specimen structure and morphology must be considered when interpreting results. Here we use ultrafast electron microscopy (UEM) imaging and diffraction to study the influence of individual multilayer terraces and few-layer step-edges on acoustic-phonon dynamics in 1T-TaS 2 and 2H-MoS 2. In TaS 2, we find that a multilayer terrace produces distinct, localized responses arising from thickness-dependent c-axis phonon dynamics. Convolution of the responses is demonstrated with ultrafast selected-area diffraction by limiting the probe size and training it on the region of interest. This results in a reciprocal-space frequency response that is a convolution of the spatially separated behaviors. Sensitivity of phonon dynamics to few-layer step-edges in MoS 2 and the capability of UEM imaging to resolve the influence of such defects are also demonstrated. Spatial frequency maps from the UEM image series reveal regions separated by a four-layer step-edge having 60.0 GHz and 63.3 GHz oscillation frequencies, again linked to c-axis phonon propagation. As with ultrafast diffraction, signal convolution is demonstrated by continuous increase of the size of the selected region of interest used in the analysis.

Original languageEnglish (US)
Pages (from-to)1877-1884
Number of pages8
JournalJournal of Physical Chemistry A
Issue number9
StatePublished - Mar 5 2020

Bibliographical note

Funding Information:
This material is based upon work supported by the National Science Foundation under Grant No. DMR-1654318. This work was partially supported by the National Science Foundation through the University of Minnesota MRSEC under Award Number DMR-1420013. This work was partially supported by the Arnold and Mabel Beckman Foundation in the form of a Beckman Young Investigator Award. Acknowledgment is made to the Donors of the American Chemical Society Petroleum Research Fund for partial support of this research. Part of this work was carried out in the College of Science and Engineering Characterization Facility, University of Minnesota, which has received capital equipment funding from the NSF through the UMN MRSEC program under Award Numbers DMR-0819885 and DMR-1420013.

Publisher Copyright:
Copyright © 2020 American Chemical Society.

MRSEC Support

  • Partial

PubMed: MeSH publication types

  • Journal Article


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