Structural limitations to local thermal diffusivities of diamond films

The photothermal displacement technique at transient thermal gratings and photothermal microscope, both providing a spatial resolution on a micrometer scale, were used to investigate the thermal properties of crystallites 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/photoluminescence spectroscopy and infrared spectroscopy. In the vicinity of a highly defective region located between crystallites, which exhibits a preferential incorporation of lion-diamond carbon, silicon-vacancy complexes and hydrogen, a reduction of the thermal diffusivity by about 35 per cent was observed. Depending upon whether this region is a grain boundary or a defect-filled microcrack, the decrease in the thermal diffusivity is 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(exp -1)K(exp -1) and 1700 W m(exp -1)K(exp -1) were determined within the crystallites at room temperature.