High pressure annealing of CVD diamond films

CVD diamond films were annealed from 600 to 1900 degreesC at 7.7 GPa in a toroidal high pressure (HP) apparatus, always inside the diamond-phase stability region. The annealed films were analyzed by Raman and infrared (IR) spectroscopy and the results showed that the diamond grains remained stable while the non-diamond carbon phases and impurities, responsible for the intricate film structure, changed after processing. For the HP annealing from 600 to 1300 degreesC, there were no major changes in the Raman spectra of the film, however, the film became easily broken and the IR spectra indicated a high reactivity of carbon with chemical elements from the environment. After annealing at 1500 degreesC and 7.7 GPa, the formation of diamond-like (DLC) and graphitic structures in-between the diamond grains were observed, while the reaction with the environment elements decreased. For higher temperatures, the DLC and graphitic structures persisted up to 1700 degreesC and the film incorporated OH in large amounts. The results showed that the non-diamond carbon species are susceptible to the HP annealing, and structural modifications in between the diamond grains are significant for temperatures above 1300 degreesC at 7.7 GPa. (C) 2003 Elsevier Science B.V. All rights reserved.