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.
| Original language | English |
|---|---|
| Article number | 065601 |
| Journal | Physical Review Materials |
| Volume | 3 |
| Issue number | 6 |
| DOIs | |
| State | Published - Jun 3 2019 |
Funding
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. 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.
| Funders | Funder number |
|---|---|
| DOE Office of Science | |
| U.S. Department of Energy | DE-AC02-06CH11357 |
| Samsung | |
| Office of Science | |
| Basic Energy Sciences | |
| Argonne National Laboratory | |
| Resnick Sustainability Institute for Science, Energy and Sustainability, California Institute of Technology | |
| Division of Materials Sciences and Engineering |