Limits to Fourier theory in high thermal conductivity single crystals

We report the results of time-domain thermoreflectance (TDTR) experiments that examine the ability of Fourier theory to predict the thermal response in single crystals when heater dimensions are small. We performed TDTR measurements on Al-coated diamond, 6H-SiC, GaP, Ge, MgO, GaAs, and GaSb single crystals with a wide range of laser spot size radii, 0.7 mu m< w(0) < 12 mu m. When the laser spot-size is large, w(0) approximate to 12 mu m, TDTR data for all crystals are in agreement with predictions of Fourier theory with bulk thermal conductivity values. When the laser spot-size is small, w(0) < 2 mu m, there are significant differences between the predictions of Fourier theory and TDTR data for all crystals except MgO. (c) 2015 AIP Publishing LLC.