PHOTOTHERMAL EXAMINATION OF THE HEAT DIFFUSION INHOMOGENEITY IN DIAMOND FILMS OF SUBMICRON THICKNESS

We present measurements of the in-plane thermal diffusivity of free-st anding diamond films of thicknesses from 0.3 to 6 mum. The phototherma l method used for the measurements is non-destructive and contact-free , and does not require any sample preparation. The measured values he in the range of 0.1 to 1.0 cm2 s-1, which is an order of magnitude bel ow typical results obtained on bulk material. The results show a stron g dependence of the thermal diffusivity on the film thickness and morp hology. Phonon scattering at grain boundaries was identified as the do minating process limiting the heat diffusion. The availability of sets of films with different characteristics allowed the determination of the spatial dependence of the heat diffusivity even in very thin membr anes. The observed effects are in good accordance with the extrapolati on of measurements previously performed on much thicker samples. The d ata are correlated to results gained by Raman spectroscopy and spectro scopic ellipsometry.