VARIATION OF THE RAMAN DIAMOND LINE-SHAPE WITH CRYSTALLOGRAPHIC ORIENTATION OF ISOLATED CHEMICAL-VAPOR-DEPOSITED DIAMOND CRYSTALS

The growth faces of large isolated chemical-vapour-deposited (CVD) diamond crystals have been studied using Raman microprobe spectroscopy. The crystals were grown on wire tips using microwave plasma chemical vapour deposition. This enables an effective study to be made of fundamental growth mechanisms by eliminating those defects and stresses associated with particle intergrowth in polycrystalline diamond thin films. A variation of the diamond line shape was observed from different growth directions of the same crystal. The [100] and [111] growth directions were sampled by focusing the laser spot onto the adjacent (100) and (111) growth faces of the same crystal. The high-resolution Raman spectra from these two growth directions exhibit different, non-symmetric 1332 cm-1 diamond line shapes. Not only is there a shift in the diamond line, but a splitting is also observed indicative of the presence of large anisotropic stresses in these crystals. Furthermore, an additional peak at about 1326 cm-1 is observed, but only when sampling the volume of the crystal underneath a (111) growth face. This 1326 cm-1 peak displays an enhanced depolarization ratio for the incident electric field vector parallel to the [112BAR] direction. The results suggest that the origin of this peak probably stems from the presence of stacking faults on {111} planes.