Frequency shift and attenuation of hypersonic surface acoustic phonons under metallic gratings

Using aluminum gratings of varying duty cycles, we report picoseconds acoustics measurements of frequency shift and attenuation in surface acoustic phonons in silicon at ∼15 GHz. We observe that the frequency shifts nonlinearly with the duty cycle, particularly in the range of 0.3 to 0.5. The data deviate from the perturbation model as a sinusoidal function of the duty cycle. The attenuation peaks at 0.5 duty cycle which is in good agreement with an eigenmode analysis of the composite structure. This work elucidates the mechanism of surface acoustic phonon scattering at periodic interfaces.