Measurement of thermal diffusivity of thin films and foils using a laser scanning microscope

Abstract

A novel method for measuring the thermal diffusivity of free-standing foils and thin films is described and has been used to measure the thermal diffusivity of gold and amorphous silicon foils. The method involves scanning the surface of the film using a sinusoidally modulated, finely focused laser beam and monitoring the thermovoltage developed at a fixed point on its surface. A thermal wave spreads out from the point where the laser spot irradiates the foil which depends only on the thermal properties of the film material and the modulation frequency. Measuring the phase of the thermovoltage, which in turn is generated due to the thermal wave, the thermal diffusivity of the films was determined. The experiments were performed in vacuum so that convective heat losses could be neglected. The thermal diffusivity of 100-nm-thick gold foils was found to be 1.17×10−4 m2/s and that of 200-nm-thick amorphous silicon foils was determined to be 0.062×10−4 m2/s.