Anomalous behaviour of surface Brillouin scattering in thin strained CVD diamond

Hellium ions were implanted into diamond at energies of 80 and 160 keV with fluences beyond the amorphization threshold using the Cold Implantation Rapid Annealing (CIRA) technique. A thin recrystallized diamond layer of ≈63 nm and ≈103 nm for implantation at 80 keV and 160 keV, respectively was estimated using the constant angle reflection interference spectroscopy. Analysis on this thin diamond-graphitic carbon-bulk diamond structure was carried out using Raman spectroscopy, diffuse reflectance spectroscopy and surface Brillouin scattering. Raman analysis shows that the damaged buried layer consists of an amorphous graphitic material while the diffuse reflectance measurements showed high reflectance at the diamond-graphitic layer interface. This led to multiple reflectivity resulting in reduction of the intensity of the incident beam to ≈0.37 that gets reflected. Surface Brillouin scattering showed a weak longitudinal peak, LKB2 at 61.6 GHz for the recrystallized diamond layer while for the unimplanted diamond a similar peak was observed at 64.2 GHz for laser beam λ = 514.5 incident at θi = 70° to the sample surface's normal. Further, surface Brillouin scattering showed an un-usual behaviour where the LKB2 peak disappeared after some time of collection. This was attributed to ‘wipe out’ phenomenon where multiple reflections resulted in multiple inelastically scattered light being detected in the recrystallized layer.