Revealing Vibrational Nonequivalence at Interfaces in Polar Heterostructures using STEM-EELS and DFT

ORAL

Abstract

Distinct material properties and emergent phenomena stem from structural and chemical discontinuities at interfaces. In heterostructures made from polar materials, e.g., piezoelectric AlN-GaN-AlN, the two interfaces are nonequivalent, hosting distinct 2D carrier gases, resulting from piezoelectric and spontaneous polarization effects. Likewise, the modes of atomic vibrations at interfaces are also affected by the corresponding structural and chemical discontinuities. The nonequivalence of these interface vibrations has not yet been investigated due to a lack of experimental techniques with both high spatial and spectral resolution. We demonstrate the nonequivalence of AlN-(Al0.65Ga0.35)N and (Al0.65Ga0.35)N-AlN interface vibrations using monochromated electron-energy-loss spectroscopy in the scanning transmission electron microscope (STEM-EELS) and explicate the physical origin of the nonequivalent interface behavior using density-functional theory (DFT). Our work leverages the mixed real- and reciprocal space selectivity of the vibrational response in angle-resolved STEM-EELS to directly map nonequivalent interface phonons between materials with different stacking order. The findings elucidate the vibrational characteristics of interfaces, which can enhance thermal conductivity.

* Theory at Vanderbilt University (H.A.W., D.-L.B., and S.T.P.) was supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Directorate grant number DE-FG02-09ER46554 and by the McMinn Endowment at Vanderbilt University. Calculations were performed at the National Energy Research Scientific Computing Center (NERSC), a US Department of Energy Office of Science User Facility located at Lawrence Berkeley National Laboratory, operated under contract number DE-AC02-05CH11231.E.R.H. and J.A.H. acknowledge support for vibrational EELS experiments from the U.S. Depart-ment of Energy (DOE), Office of Basic Energy Sciences (BES), Division of Materials Sciences and Engineering and the Center for Nanophase Materials Sciences, a U.S. DOE Office of Science User Facility at Oak Ridge National Laboratory.E.R.H., J.A.H., and J.B. acknowledge support for 4D-STEM and mechanical cross-section sample preparation performed as part of user proposal CNMS2023-B-02088 at the Oak Ridge National Laboratory (ORNL), the Center for Nanophase Materials Sciences (CNMS), which is a US De-partment of Energy Office of Science User Facility. Microscopy performed using instrumentation within ORNL's Materials Characterization Core provided by UT-Battelle, LLC, under Contract No. DE-AC05- 00OR22725 with the DOE and sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U

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Publication: Hoglund, E. , Walker, H., Hussain, K., Bao, D., Ni, H. , Baxter, J., Khan, A., Pantelides, S. Hopkins, P. Hachtel, J. (2023). Non-equivalent Atomic Vibrations at Interfaces in a Piezoelectric Superlattice. Nature Materials. (Manuscript pre-approved for submission)

Presenters

  • Harrison A Walker

    Interdisciplinary Materials Science Program, Vanderbilt University

Authors

  • Harrison A Walker

    Interdisciplinary Materials Science Program, Vanderbilt University

  • Eric R Hoglund

    Oak Ridge National Laboratory

  • Deliang Bao

    Vanderbilt University, Department of Physics and Astronomy, Vanderbilt University

  • Kamal Hussain

    University of South Carolina

  • Haoyang Ni

    Oak Ridge National Laboratory

  • Jefferey Baxter

    Oak Ridge National Laboratory

  • Asif W Khan

    Univ of South Carolina

  • Patrick E Hopkins

    Univ of Virginia

  • Jordan A Hachtel

    Oak Ridge National Laboratory, Center for Nanophase Materials Sciences, Oak Ridge National Laboratory

  • Sokrates T Pantelides

    Department of Physics and Astronomy, Vanderbilt University