Thermal diffusivity of diamond/Si composite films measured by an ac calorimetric method

In measurenlents of thermal dill"usivity, by an ac calorimetry method, on films of materials of high thermal diflʹusivity, attention should be paid to the effects of the sample length, i,e,, the reflection of ac temperature waves at the sample edge, For such a case, the apparent thermal diffusivity of the sample having a finite length is given analytically us a function of frequency. Measurements were performed on diamond/Si composite Iilms. The overall behavior of the frequency dependence of the apparent thermal diflʹusivity obtained is satisfactorily cxplained by the analytical expression. The true thermal diflʹusivity is obtained by litting a theoretical curve to the experimental results. Especially when the apparent thermal diffusivity saturates in a high-frequency region, the saturated value gives the true thermal diffusivity.