Analytical inversion of photothermal measurements: Independent determination of the thermal conductivity and diffusivity of a conductive layer deposited on an insulating substrate

The long distance behavior of the surface temperature wave in a thermoreflectance microscopy experiment is established for a conductive layer deposited on an insulating substrate. At large distance from the point source, heat is confined, so the amplitude decrease is lower than for a bulk sample. From the slopes which appear on the phase and on the log scale amplitude, a procedure is proposed to extract, separately, the thermal diffusivity and conductivity of the layer, taking into account data obtained at different modulation frequencies. Experimental results are presented which confirm the validity of the method. (C) 2007 American Institute of Physics.