Thermal acoustic excitations with atomic-scale wavelengths in amorphous silicon
Abstract
The vibrational properties of glasses remain a topic of intense interest due to several unresolved puzzles, including the origin of the Boson peak and the mechanisms of thermal transport. Inelastic scattering measurements have revealed that amorphous solids support collective acoustic excitations with low THz frequencies despite the atomic disorder, but these frequencies are well below most of the thermal vibrational spectrum. Here, we report the observation of acoustic excitations with frequencies up to 10 THz in amorphous silicon. The excitations have atomic-scale wavelengths as short as 6 Å and exist well into the thermal vibrational frequencies. Simulations indicate that these high-frequency waves are supported due to the high group velocity and monatomic composition of a-Si, suggesting that other glasses with these characteristics may also exhibit such excitations. Our findings demonstrate that a substantial portion of thermal vibrational modes in amorphous materials can still be described as a phonon gas despite the lack of atomic order.
Additional Information
© 2019 American Physical Society. Received 4 February 2019; revised manuscript received 6 May 2019; published 3 June 2019. The authors thank Nathan Sangkook Lee for helpful discussions in sample preparations, Dr. Jörg Neuefeind and Michelle Everett for assistance in data collection at NOMAD, and Dr. Bianca Haberl for helpful discussions. The authors thank Dr. John Budai for assistance in data collection at HERIX-30. This work was supported by a Samsung Scholarship and a Resnick Fellowship from the Resnick Sustainability Institute at Caltech, and the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. A portion of this research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. This paper has been co-authored by employees of UT-Battelle, LLC, under Contract No. DE AC0500OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this paper, or allow others to do so, for the United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan. J.M. and A.J.M. conceived the project. J.M. synthesized the a-Si samples. J.M., A.A., A.H.S, R.P.H., and M.E.M conducted the IXS experiments and analyzed the results. R.P.H. performed the RDF measurements. J.M. performed molecular dynamics calculations. J.M. and A.J.M. wrote the paper with input from all authors. A.J.M. supervised the project. The authors declare no competing interests.Attached Files
Published - PhysRevMaterials.3.065601.pdf
Supplemental Material - Supplementaryt.pdf
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Additional details
- Eprint ID
- 96026
- Resolver ID
- CaltechAUTHORS:20190603-091248429
- Samsung Scholarship
- Resnick Sustainability Institute
- DE-AC02-06CH11357
- Department of Energy (DOE)
- DE-AC05-00OR22725
- Department of Energy (DOE)
- Created
-
2019-06-03Created from EPrint's datestamp field
- Updated
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2021-11-16Created from EPrint's last_modified field
- Caltech groups
- Resnick Sustainability Institute