Nanoscale Phonon Spectroscopy Reveals Emergent Interface Vibrational Structure of Superlattices

Eric Hoglund^a, De-Liang Bao^b, Andrew O'Hara^b, Jordan Hachtel^c, Zachary Piontkowski^d, Joseph Matson^l, Ajay Yadav^e, Ryan Haisimaier^f, Roman Engel-Herbert^f, Jon Ihlefeld^a, Jayakanth Ravichandran^g, Ramamoorthy Ramesh^e, Joshua Caldwell^l, Thomas Beechem^d^,^h, Sokrates Pantelides^b^,ⁱ, Patrick Hopkins^j^,^k, James Howe^a

^aMaterials Science and Engineering, University of Virginia

^bDepartment of Physics and Astronomy, Vanderbilt University, Vanderbilt Place, Nashville, United States

^cCenter for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, EE. UU., Oak Ridge, United States

^dSandia National Laboratories

^eDepartment of Materials Science and Engineering, University of California Berkley

^fDepartment of Materials Science and Engineering, Pennsylvania State University, 221 Steidle Building University Park, State College, United States

^gDepartment of Chemical Engineering and Materials Science, University of Southern California, Bloom Walk, 925, Los Angeles, United States

^hCenter for Integrated Nanotechnologies, Sandia National Laboratories,

ⁱDepartment of Electrical Engineering and Computer Science, Vanderbilt University, Vanderbilt Place, 2301, Nashville, United States

^jDepartment of Mechanical and Aerospace Engineering, University of Virginia, McCormick Road, 351, Charlottesville, United States

^kDepartment of Physics, University of Virginia, McCormick Road, 382, Charlottesville, United States

^lDepartment of Mechanical Engineering and Electrical Engineering, Vanderbilt University, Nashville, United States

Proceedings of Electron Beam Spectroscopy for Nanooptics 2021 (EBSN2021)

Online, Spain, 2021 June 14th - 15th

Organizers: Mathieu Kociak and Nahid Talebi

Poster, Eric Hoglund, 051
Publication date: 8th June 2021

ePoster:

Perovskite oxides offer an abundance of properties with technological importance that are tunable by creating superlattices (SLs). Most research so far focuses on electronic properties, but such SLs can also feature unique thermal properties, which are dictated by lattice vibrations. Here we combine atomic-resolution integrated differential phase contrast in a scanning transmission electron microscopy, vibrational electron energy-loss spectroscopy, and density-functional-theory calculations to probe the phonon spectra and oxygen atom positions for a series of SrTiO₃-CaTiO₃SLs with one to twenty-seven unit-cells per layer. We show large-period SLs feature bulk plus localized interface vibrational modes. As layer thickness decreases, the bulk modes disappear while the interface modes underpin an emergent phonon structure, which is also reflected in the macroscopic vibrational response measured by UV-Raman and Fourier transform infrared spectroscopy. This behavior correlates to period thickness reaching the length scale of TiO₆ octahedral coupling at the interfaces, thus reflecting the dominant role of interfaces as size decreases and the need for spatially quantified structural and vibrational data to enable complete understanding of SL behavior.

Acknowledgements:

ERH and PEH appreciate support from the Office of Naval Research through a MURI Program, Grant Number N00014-18-1-2429. Theory at Vanderbilt University was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Directorate grant No. DE-FG02-09ER46554 and by the McMinn Endowment. Calculations were performed at the National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility located at Lawrence Berkeley National Laboratory, operated under Contract No. DE-AC02-05CH11231.

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