Understanding the emergence of the boson peak in molecular glasses. González-Jiménez, M., Barnard, T., Russell, B., Tukachev, N., Javornik, U., Hayes, L., Farrell, A., Guinane, S., Senn, H., Smith, A., Wilding, M., Mali, G., Nakano, M., Miyazaki, Y., McMillan, P., Sosso, G., & Wynne, K. December, 2022.
Paper doi abstract bibtex A common feature of glasses is the “boson peak”, observed as an excess in the heat capacity over the crystal or as an additional peak in the terahertz vibrational spectrum. The microscopic origins of this peak are not well understood; the emergence of locally ordered structures has been put forward as a possible candidate. Here, we show that depolarised Raman scattering in liquids consisting of highly symmetric molecules can be used to isolate the boson peak, allowing its detailed observation from the liquid into the glass. The boson peak in the vibrational spectrum matches the excess heat capacity. As the boson peak intensifies on cooling, wide-angle x-ray scattering shows the simultaneous appearance of a pre-peak due to molecular clusters consisting of circa 20 molecules. Atomistic molecular dynamics simulations indicate that these are caused by over-coordinated molecules. These findings represent an essential step toward our understanding of the physics of vitrification.
@misc{gonzalez-jimenez_understanding_2022,
title = {Understanding the emergence of the boson peak in molecular glasses},
url = {https://chemrxiv.org/engage/chemrxiv/article-details/639b24dae9d0fd62f41df5f7},
doi = {10.26434/chemrxiv-2022-25q9h-v4},
abstract = {A common feature of glasses is the “boson peak”, observed as an excess in the heat capacity over the crystal or as an additional peak in the terahertz vibrational spectrum. The microscopic origins of this peak are not well understood; the emergence of locally ordered structures has been put forward as a possible candidate. Here, we show that depolarised Raman scattering in liquids consisting of highly symmetric molecules can be used to isolate the boson peak, allowing its detailed observation from the liquid into the glass. The boson peak in the vibrational spectrum matches the excess heat capacity. As the boson peak intensifies on cooling, wide-angle x-ray scattering shows the simultaneous appearance of a pre-peak due to molecular clusters consisting of circa 20 molecules. Atomistic molecular dynamics simulations indicate that these are caused by over-coordinated molecules. These findings represent an essential step toward our understanding of the physics of vitrification.},
language = {en},
urldate = {2023-01-10},
publisher = {ChemRxiv},
author = {González-Jiménez, Mario and Barnard, Trent and Russell, Ben and Tukachev, Nikita and Javornik, Uroš and Hayes, Laure-Anne and Farrell, Andrew and Guinane, Sarah and Senn, Hans and Smith, Andrew and Wilding, Martin and Mali, Gregor and Nakano, Motohiro and Miyazaki, Yuji and McMillan, Paul and Sosso, Gabriele and Wynne, Klaas},
month = dec,
year = {2022},
keywords = {DFT, FTIR, Raman, Vogel-Fulcher-Tammann, WAXS, boson peak, calorimetry, glass transition, molecular dynamics, optical Kerr effect, ssNMR, structure, supercooling, terahertz, viscometry, vitrification},
}
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