Specific heat of single-, poly- and nanocrystalline diamond

Measurements of the specific heat C(p) were performed on several CVD-diamond samples, type IIb single-crystal diamond and on an amorphous carbon film in a differential scanning calorimeter between room temperature and 300 degrees C. The C(p) measurement results of the CVD diamond samples were only weakly affected by the grain size ranging from 20 nm to 100 mu m, by the film thickness ranging from 300 nm to 300 mu m and by the hydrogen concentration ranging from <1 to 10 at.%. The specific heat of single-crystal diamond of 0.54 J g K(-1) at 50 degrees C is similar to the coarse-grained diamond film, but differs slightly from the specific heat of the nanocrystalline diamond film of 0.68 J g K(-1). Compared to the diamond samples the specific heat of an amorphous carbon him with a hydrogen concentration of 30 at.% was found to be increased by 0.5 J g K(-1). These results justify the assumption that the specific heat of polycrystalline CVD diamond samples is similar to their single-crystalline counterparts. In the case of pure amorphous carbon films this assumption is no longer valid. (C) 1998 Elsevier Science S.A.