Abstract
We studied the acoustic properties at sub-THz frequencies of SiO_2 amorphous thin films. SiO_2 amorphous thin films were prepared by reactive sputtering of Si target in argon/oxygen mixture with various conditions. We measured Brillouin oscillation frequency using a femtosecond pump-probe method. We determined the longitudinal sound velocity from measured frequency and refractive index measured by ellipsometry. The results show that the velocities of SiO_2 amorphous thin films highly depend on the microstructure such as microcracks and texture. Thus, this indicates that Brillouin oscillation technique is an effective tool of evaluation for not only acoustic properties but also reliability for transparent materials.
