We have investigated the feasibility of phonon-reflection techniques as non-destructive means to probe surface and/or near-surface damage in otherwise highly perfect crystals. A UHV liquid-helium stage, suitable for phonon-reflection measurements, was installed on a beam line of a tandem van de Graaff accelerator which was used to implant MeV ions into the substrate in order to modify the subsurface region in situ. Here, we report our investigation on the effects of 1 MeV Ar⁺ implantation in Al₂O₃ single crystals by monitoring the reflection of terahertz (THz) phonons (50 Å wavelength) from the implanted region. The results are supported by x-ray rocking measurements and Monte Carlo simulations.
Using a 15 kV ion gun on the same beam line we have also bombarded Al₂O₃ crystals coated with thin films of gold. The effects of a 7.5 keV Ar⁺ irradiation on this Au - Al₂O₃ system are also discussed in this thesis.
The relevance of this work is discussed in connection to the observations made by other groups and also to our previous work (reported in Appendix 3) on phonon-induced desorption of He atoms as well as the Kapitza anomaly.
