Measurement of thermal diffusion in thin films using a modulated laser technique: Application to chemical-vapor-deposited diamond films

A method to determine the thermal diffusivity in thin films, based on the measurement and analysis of thermal waves induced by a modulated infrared laser, is demonstrated. A nearly exact mathematical description, independent of the film geometry and including surface heat losses, is presented. It is shown that the in-plane thermal diffusivity and the heat loss through the surface can be determined independently by analysis of both the phase and the amplitude of the thermal waves. The validity of the method has been verified using high-purity copper sheets of varying thickness, for different modulation frequencies. Several polycrystalline, chemical-vapor-deposited (CVD) diamond films have been investigated. The measurements were performed both on free-standing films and on two-layer systems of CVD diamond and copper. Thermal diffusivities for polycrystalline diamond up to 6.2 cm2 s−1 were recorded.