Porosity Dependence of the Velocity of Surface and Bulk Acoustic Waves in Porous Silicon Carbide Films

Abstract

Brillouin light scattering spectroscopy was used to probe porous silicon carbide films formed from p-type 6H crystalline silicon carbide. The porosities of the films ranged from 30% to 58%. Surface and bulk acoustic wave velocities were measured and compared with those calculated from the Mori-Tanaka acoustic effective medium model. Qualitative agreement is obtained between the experimentally determined velocities and those predicted by Mori-Tanaka acoustic effective medium models with spherical pores and, in the case of surface acoustic waves, also with prolate spheroidal pores with shape factor equal to 0.2. The model demonstrates the importance of morphology in determining the behavior of acoustic waves in a porous material.

Elastic Waves in Nano-Columnar Porous 4H-SiC Measured by Brillouin Scattering

“…The data reported here were obtained in backscattering geometries (φ = 180°), with the incident and scattered radiation propagating parallel or perpendicular to the optical axis. Note that we neglected optical anisotropy in our previous work [2] on bulk acoustic waves in porous 6H SiC.…”

“…Here, we present a comparison between the measured frequencies (which can be converted to speeds) of elastic waves and the predictions of an effective medium model for nanocolumnar porous 4H-SiC, a mesoporous material of sufficiently simple microstructure that analytic expressions for the effective elastic properties can be developed in the long wavelength (quasistatic) limit. In our previous work on bulk and surface acoustic waves in porous p-type 6H SiC [1,2], the relationship of the effective medium model, based on a microstructure of oriented ellipsoidal cavities, to the actual porous morphology is less direct.…”