Abstract
In this study, we have extracted the phonon mean free path of low thermal conductivity materials by time-domain thermoreflectance measurements with gold nanoislands. Firstly, 7 and 9 nm thick gold films were deposited on the material substrate by vacuum evaporation method, and then annealed at 500 ℃ and 900 ℃ to form gold nanoislands with various size-distributions. This realizes variation of the average contact area between the nanoislands and substrate. Secondly, the size-dependent thermal conductivity is obtained by time-domain thermoreflectance using femto-second laser beams: the gold nanoislands were heated up by the pump beam and its temporal thermal response by the probe beam, while the substrate is transparent to the beams. The size-dependent thermal conductivity values of fused quartz and sapphire agree with the solutions of the Boltzmann transport equation, from which the characteristic phonon mean free path can be obtained.
