A new approach to measure the cross-plane thermal diffusivity of a microscale slab sample, which can be fabricated by the focused ion beam and attached to a substrate, is proposed. An intensity-modulated pump laser is applied to heat the front surface of the sample uniformly, and the thermoreflectance signal is observed at the rear surface to evaluate thermal wave transport in the material. The thermal diffusivity can be obtained by fitting the phase lags of the experimental data with a theoretical model. The model was developed for the sample with thin-film coatings and heat transfer to the substrate. Although the absorbed heat can cause a significant DC temperature increase in the microscale sample, a thin-film coating with high thermal conductivity can effectively reduce the DC temperature increase within low thermal conductivity samples. To validate the method, we conducted measurements of a fused silica sample of 2.16 µm thickness, coated with 95 nm Ti film on the front surface and 120 nm Au film on the rear surface. The measured thermal diffusivity is in good agreement with the literature value. The uncertainty analysis shows that the measurement uncertainty is within 6%. This proposed approach, designed for microscale samples, offers a unique option for thermal property measurements of special materials, such as irradiated nuclear fuel or other irradiated materials, to enable microscale property determination while minimizing sample radioactivity.
This study develops an infrared radiometry-based steady-state technique (SSIR) that combines the benefits of transient pump technique, steady-state method, and infrared radiometry. The method uses a continuous wave (CW) laser as the pump source and a high-speed infrared camera system to capture temperature-time maps as the probe system. Instead of the thermoreflectance measurement, the advanced infrared camera system eases the theoretical model and experiment. The infrared camera system enables straightforward temperature versus time reading with a good spatial resolution. For demonstration, material with thermal conductivity over two orders of magnitude (1∼150Wm−1K−1) are measured. This technique enables measuring thermal conductivity independently from volumetric heat capacity, and by using reference sample, the sensitivity to most input parameters is effectively reduced. Therefore, SSIR shows lower uncertainty to standard FDTR and TDTR.
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