Thermal diffusivity and effusivity of thin layers using time-domain thermoreflectance

Analytical expressions for the thermal diffusivity and effusivity of thin layers starting from the time-domain thermoreflectance are proposed. These relations rest on the analytical solution of one-dimensional heat transfer in the medium using integral transforms. For noncapped layers, asymptotic behaviors of the impulse response lead to the analytical expression of the thermal diffusivity according to the optical properties of the medium. In case of metals, the two-temperature model shows that the capacitance effect at the small times is essentially governed by the electronic contribution. For capped layers with an aluminum film, an analytical expression of the thermal effusivity of the layer is derived. The particular influence of the heat penetration depth in the aluminum film during the thermalization between the electron gas and the lattice is demonstrated.