Effective thermal diffusivity of layered materials measured by modulated photothermal techniques

Abstract

Modulated photothermal techniques provide useful methods based on linear relations to measure the thermal diffusivity of homogeneous materials. We have analyzed theoretically the applicability of such linear relations to two particular cases of layered composites, i.e., two-layer materials and superlattices. In order to measure the through-thickness and in-plane thermal diffusivities of these anisotropic materials, planar and pointlike excitations have been studied. The main result of this article is that the linear relations encountered for homogeneous materials still hold for layered composites, although their slopes do not always give the effective thermal diffusivities of the sample parallel and perpendicular to the layers, as derived from the in-parallel and in-series thermal resistors models, respectively. However, an “apparent” thermal diffusivity is obtained from which the thermal parameters of each layer can be retrieved.