Abstract
Phonon dynamics and transport determine how heat is utilized and dissipated in materials. In 2D systems for optoelectronics and thermoelectrics, the impact of nanoscale material structure on phonon propagation is central to controlling thermal conduction. Here, we directly observe in-plane coherent acoustic phonon propagation in black phosphorus (BP) using ultrafast electron microscopy. We identify a significant reduction of the group velocities in directions intermediate to the armchair and zigzag lattice directions. Using a machine learning-based model with an >8000 atom supercell, we find that this slowing results from the mixing of in-plane transverse and longitudinal acoustic phonons and is independent of broken symmetries of edge reconstructions. This work demonstrates how coherent phonon transport is sensitive to propagation direction in the lattice plane.
| Original language | English |
|---|---|
| Pages (from-to) | 4324-4332 |
| Number of pages | 9 |
| Journal | ACS Nano |
| Volume | 19 |
| Issue number | 4 |
| DOIs | |
| State | Published - Feb 4 2025 |
Funding
The authors thank Dr. Karen M. Watters for the scientific editing of the manuscript, Dr. Eva Pogna for her helpful discussions regarding her inelastic X-ray scattering experiments, and Dr. Michael Spencer and Dr. Joanna Urban for numerous helpful discussions. This work was funded by the Office of Basic Energy Sciences, U.S. Department of Energy (Grant No. DE-SC0021950). Work performed at the Center for Nanoscale Materials, a U.S. Department of Energy Office of Science User Facility, was supported by the U.S. DOE, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. This work made use of the shared facilities at the University of Chicago Materials Research Science and Engineering Center, supported by the National Science Foundation under award number DMR-2011854. This work was completed in part with resources provided by the University of Chicago’s Research Computing Center. P.P.J. acknowledges support from a MRSEC-funded Kadanoff-Rice fellowship (DMR-2011854 and DMR-1420709). D.G.U. and M.K.Y.C. acknowledge the support from the BES SUFD Early Career award. R.L. acknowledges support from an MRSEC-funded graduate research fellowship (DMR-1420709). S.B.K. acknowledges start-up funding support from the University of Chicago and the Neubauer Family Assistant Professors Program. L.L. was supported by the Center for Nanophase Materials Sciences (CNMS), which is a U.S. Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory.
Keywords
- black phosphorus
- lattice anisotropy
- phonon transport
- thermoelectrics
- ultrafast electron microscopy