Thermal diffusivity measurements based on laser induced heat transfer in low-conductivity thin films

Original experimental method for evaluation of thermal diffusivity coefficient of vacuum deposited thin films with low thermal conductivity is presented. For this purpose three-layered samples are vacuum deposited onto precleaned glass substrate. Thin film of TeO2 or NaCl respectively is sandwiched between array of connected in series thin film thermocouples at the bottom and metal layer at the top. Nd:YAG laser radiation (lambda= 1064nm, tau= 12ns) absorbed in the metal layer is used to create beat pulse in the sample. The heat released is transferred to the thermocouple array through the film studied with a delay proportional to thermal diffusivity of the sandwiched material. Further, a simple relation between the thermal diffusivity coefficient, film thickness and time of the thermoelectric response delay is used to estimate the thermal diffusivity of NaCl or TeO2 thin film. A relationship between the thermal properties and the microstructure of the film studied is revealed. Finally, it is demonstrated that the method applied is appropriate for studying of any thin film material with low thermal conductivity.