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Slightly graphitization might be incurred on CVD diamond films when suffering instantaneous high temperature thermal shock. In this paper, phase transitions of CVD free-standing diamond films have been studied experimentally at the temperature range of 1500–1800 °C through a plasma rapid heating process. Raman spectra and X-ray photoelectron spectra (XPS) are compared and discussed for the purpose of measuring the percentage of graphitic carbon component in CVD diamond films after heat treatment at different temperatures. An obvious optical degradation took place in both visible and infrared bands with the increased treating temperature. The result indicates that graphitization is dominated along grain boundaries rather than in internal grains. In addition, the nitrogen related absorption peaks were not covered by the enhanced optical absorption background, which was caused by the opaque graphitic carbon formed at high temperature. Nitrogen concentrations have also been evaluated for these graphitized diamond films and there is no evidence to show the movement or aggregation of nitrogen atoms. [ABSTRACT FROM AUTHOR]

Polycrystalline CVD free-standing diamond films have been heat treated through a rapid heating process using a direct current (DC) arc plasma jet system within the temperature range of 1500–2000 °C. The optical transmission of the diamond film decreases when the treatment temperature exceeds 1500 °C. When the diamond film was annealed to 1800 °C for just 1 min, the infrared (IR) transmittance at λ = 10.6 μm of the film was significantly decreased from 60.5% to 4.0%, due to the transformation from diamond to graphite. Further increase of the temperature to 2000 °C leads to complete loss of optical transmittance in only 30 s, due to the detrimental occurrence of graphitization. XRD patterns indicate that graphite ultimately grows preferentially along the (0002) plane by forming disordered or turbostratic graphite as intermediate product. Raman spectra and SEM images verify that at 1500–1850 °C graphitic carbon transforms from the diamond surface in the form of protruding submicron crystallites, which were still containing a number of sp 3 C C bonds. In addition to graphitization on the external surface, the diamond-graphite phase transition also occurs along the grain boundaries and the calculated activation energy of the grain boundary graphitization process is 276 kJ·mol − 1 for the CVD diamond. [ABSTRACT FROM AUTHOR]