STRUCTURAL LIMITATIONS TO LOCAL THERMAL DIFFUSIVITIES OF DIAMOND FILMS

The photothermal displacement technique at transient thermal gratings and photothermal microscopy, both providing a spatial resolution on a micrometer scale, were used to investigate the thermal properties of c rystallites and regions located between crystallites of diamond grown by microwave plasma chemical vapour deposition. The thermal properties are related to the structural properties by micro-Raman/photoluminesc ence spectroscopy and infrared spectroscopy. In the vicinity of a high ly defective region located between crystallites, which exhibits a pre ferential incorporation of non-diamond carbon, silicon-vacancy complex es and hydrogen, a reduction of the thermal diffusivity by about 35% w as observed. Depending upon whether this region is a grain boundary or a defect-filled microcrack, the decrease in the thermal diffusivity i s caused by enhanced phonon scattering from these defects accumulated at the boundary or by a vanishing transmission probability of phonons across the crack. High thermal conductivities between 1500 W m(-1)K(-1 ) and 1700 W m(-1)K(-1) were determined within the crystallites at roo m temperature.