Low-frequency Raman spectrum of 2D layered perovskites: Local atomistic motion or superlattice modes?
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044710_1_online.pdf
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Published version
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3.34 MB
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Author(s)
Dahod, Nabeel S
France-Lanord, Arthur
Paritmongkol, Watcharaphol
Grossman, Jeffrey C
Tisdale, William A
Date Issued
July 28, 2020
Journal
The Journal of Chemical Physics
Publisher
AIP Publishing
Citation
Nabeel S. Dahod, Arthur France-Lanord, Watcharaphol Paritmongkol, Jeffrey C. Grossman, William A. Tisdale; Low-frequency Raman spectrum of 2D layered perovskites: Local atomistic motion or superlattice modes?. J. Chem. Phys. 28 July 2020; 153 (4): 044710.
Version
Final published version
Abstract
We report the low-frequency Raman spectrum (ω = 10 cm−1–150 cm−1) of a wide variety of alkylammonium iodide based 2D lead halide perovskites (2D LHPs) as a function of A-site cation (MA = methylammonium and FA = formamidinium), octahedral layer thickness (n = 2–4), organic spacer chain length (butyl-, pentyl-, hexyl-), and sample temperature (T = 77 K–293 K). Using density functional theory calculations under the harmonic approximation for n = 2 BA:MAPbI, we assign several longitudinal/transverse optical phonon modes between 30 cm−1 and 100 cm−1, the eigendisplacements of which are analogous to that observed previously for octahedral twists/distortions in bulk MAPbI. Additionally, we propose an alternative assignment for low-frequency modes below this band (<30 cm−1) as zone-folded longitudinal acoustic phonons corresponding to the periodicity of the entire layered structure. We compare measured spectra to predictions of the Rytov elastic continuum model for zone-folded dispersion in layered structures. Our results are consistent across the various 2D LHPs studied herein, with energetic shifts of optical phonons corresponding to microscopic structural differences between materials and energetic shifts of acoustic phonons according to changes in the periodicity and elastic properties of the perovskite/organic subphases. This study highlights the importance of both the local atomic order and the superlattice structure on the vibrational properties of layered 2D materials.
MIT Department
Massachusetts Institute of Technology. Department of Electrochemical Engineering
Massachusetts Institute of Technology. Department of Materials Science and Engineering
Massachusetts Institute of Technology. Department of Chemistry
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DOI of Published Version
https://doi.org/10.1063/5.0012763
