High-temperature Raman study in CVD diamond

Measurements of the Raman spectra in chemical vapour deposition (CVD) diamond films at temperatures up to 1200 K are presented. Specifically, the evolution of Raman line position, line width, and intensity were monitored as a function of heating time. The red shifting and the line width broadening of CVD diamond's Raman line with temperature are very similar to that of natural diamond's. However, the detailed temperature dependence of Raman line width depends on the orientation of the CVD diamond crystal and the ambient gas used during thermal treatment. Since the CVD diamond usually exhibited a broader Raman spectra than natural diamond, the evolution of the line width upon heating is thus expected to depend on the origins and the annealing effects of the residual stress. For (111) CVD diamond subjected to annealing in air at 973 K, the line width decreased by more than one wavenumber while the line intensity increased by more than an order of magnitude before it decreased subsequently. In contrast, there is hardly any observable changes of the line width for (100) CVD diamond heated in air at 1173 K. Measurements conducted in He versus in air suggested that the reduction of the non-diamond carbon phase (therefore, the reduction of stress) is likely due to oxidation, which occurs more readily in (111) than in (100).