Photothermal dielectric spectroscopy: A novel technique for the determination of the dielectric, pyroelectric and thermal properties of thin dielectric films

A novel technique is described which combines dielectric measurements with a time and frequency dependent photothermal excitation. The sample, a thin metallized film, is placed in an aluminium ring which serves as a heat sink. At different temperatures both the dielectric and pyroelectric spectra are obtained by applying sequentially an AC-voltage and a modulated heat flux to the sample. The thermal properties are assessed by the application of a local laser heating; the resulting increase in the mean sample temperature is recorded by high precision capacitance measurements at a fixed frequency. From the equilibrium increment ΔC(T) and the temperature dependence of the capacitance C(T) we can find the temperature increment ΔT(T) and thus the thermal conductivity, while from the transient response ΔC(T,t) the thermal diffusivity can be obtained. Combination of all information further yields the pyroelectric coefficient and the specific heat. Experiments on PVDF were performed at temperatures from -60 to 110°C to show the capabilities of the new method