Measurement of thermophysical properties of hydrogenated amorphous carbon thin films using picosecond thermoreflectance technique

The thermophysical properties of hydrogenated amorphous carbon (a-C:H) thin films, namely the thermal diffusivity α, thermal effusivity É, thermal conductivity κ and volumetric heat capacity C_f have been measured simultaneously using ultrafast optical pump-probe technique. The pump-probe method utilizes the film surface temperature decay following a heating pulse from a pump laser. From the temperature decay, the thermal diffusivity α and effusivity É were obtained by curve-fittings of two different physical models. The thermal conductivity κ and volumetric heat capacity C_f were then deduced from the measured α and É using the relations κ = α^1/2É and C _f = É/α^1/2. The thermal conductivity and volumetric heat capacity obtained compare favorably with those reported in the literatures. The method is independent of substrate and Al capping layers. The curve-fittings are simpler because independent of parameters of the films and the Kapitza boundary thermal resistance at Al/a-C:H interface.