Thermal conductivity of transparent thin films/substrates measured by photothermal reflectivity probing method

Abstract
In this article the photothermal reflectivity probing method is used to evaluate the thermal properties of a transparent thin film deposited on an opaque substrate. In this method the thin film is illuminated with a modulated and focused laser beam, which induces thermal waves penetrated into the sample. The resulted temperature oscillations and surface vibrations can be measured using a probe laser beam through optical reflectivity variations. According to the analytical formulas for the reflectivity of light focused on a transparent thin film/opaque substrate structure, the thermal conductivity of the thin film can be obtained by fitting the experimental frequency dependence of the reflectance signal. The validity of the method is proved by application to thin transparent ZnO films on opaque silicon substrates.