  Using a high-resolution X-Ray diffraction measurement method, the surface
acoustic waves (SAW) propagation in a graphene film on the surface of a
Ca3TaGa3Si2O14 (CTGS) piezoelectric crystal was investigated, where an external
current was driven across the graphene film. Here we show for the first time
that the application of the DC field leads to a significant enhancement of the
SAW magnitude and, as a result, to amplification of the diffraction satellites.
Amplification of 33.2 dB/cm for the satellite +1, and of 13.8 dB/cm for the
satellite +2, at 471 MHz has been observed where the external DC voltage of
+10V was applied. Amplification of SAW occurs above a DC field much smaller
than that of a system using bulk semiconductor. Theoretical estimates are in
reasonable agreement with our measurements and analysis of experimental data
for other materials.
