In-plane thermal diffusivity measurement of highly thermal conductive thin films by the flash method

The flash method has been extended to measure thermal diffusivity in the radial direction of free-standing thin films with substantial surface heat losses. A small doughnut shape portion of the front surface of the sample is exposed to the laser light and resulting temperature rise is recorded on a small radius area on the opposite side of the sample. The thermal diffusivity is calculated using a new mathematical model based on so called “fin approximation”, when the axial temperature gradient in the sample is negligible small in comparison with the radial gradient. The technique was experimentally verified on OFHC Copper with foils of available thicknesses ranging from 25μm to 0.5mm and the results are in good agreement with the TPRC recommended data within 5%. The measurement on a graphite thin film sample with the thickness of 35μm was then carried out.