Transient reflecting grating for sub-surface analysis: GHz ultrasonic and thermal spectroscopies and imaging

Picosecond time-resolved Transient Reflecting Grating (TRG) measurements are demonstrated for GHz ultrasonic and thermal spectroscopies of thin films and sub-surface regions of sub-μm scale. The measurements should be tools for electrochemical interface monitoring and time-resolved imaging. Some results are presented to show ion-implantation-induced surface hardening and unusual heat-diffusion behavior near a silicon surface. A model describing potential dependence of TRG responses at an electrochemical interface is proposed. An image of photoexcited carrier density is compared with a thermal image for a He-ion-implanted silicon wafer to demonstrate the time-resolved imaging.