Hypersound Attenuation in Amorphous Materials Measured by Femtosecond Acoustics
Tsung-Chi Hung1, Yu-Ru Huang1, Jinn-Kong Sheu2, Chi-Kuang Sun1*
1Institute of Photonics and Optoelectronics, National Taiwan University, Taipei, Taiwan
2Institute of Electro-Optical Science and Engineering, National Cheng Kung University, Tainan, Taiwan
* presenting author:Chi-Kuang Sun, email:sun@ntu.edu.tw
Amorphous materials exist many different thermal properties from their crystalline counterparts. The reduced density of vibrational states around 1 THz shows a peak, termed boson peak, disobeying the Debye model while its origin is still under debate. This “Boson peak” is often related to the abnormal behavior of heat transportation in the amorphous material whose mechanism remains controversial since lacking the experimental data of hypersond attenuation from a few hundred GHz to 1 THz.
In this presentation, making use of the femtosecond acoustics, hypersound attenuation spectra of vitreous silica film was measured starting form a few GHz to 1 THz. This compelling experiment result shows that the f2 dependency of hypersound attenuation turns into a f4 dependency between 700 GHz to 1 THz, corresponding to the observed phonon frequencies inside the Boson peak. Combining with previous theoretical studies and X-ray scattering studies, our direct measurements supports the model that Rayleigh-like scattering is the dominant loss mechanism for Boson peak phonon transport in amorphous materials at room temperature.

Keywords: phonon transport, amorphous material, hypersound