Subnanosecond transient-reflecting-grating measurements and depth-profiling analysis of mesoscopic subsurface properties of a nickel single crystal

Subnanosecond transient reflecting grating measurements were made for a mirror-polished (110) surface of a Ni single crystal under temperature control from 93-273 K and with a variety of grating spacings from 1-4 μm. The experimental responses were compared with theoretically calculated ones. Agreement was good for large grating spacings and at room temperature, but larger deviations appeared as temperature was lower or grating spacing was made smaller. The results suggested that the mesoscopic subsurface region of a submicrometer size had a different thermal diffusivity from the bulk material. The measured responses were analyzed to deduce temperature dependence of thermal diffusivity as well as acoustic velocity in the subsurface region. A depth profiling analysis of the thermal diffusivity was carried out to allow discussion of mechanisms of the diffusivity decrease.