EPR and optical studies on polycrystalline diamond films grown by chemical vapor deposition and annealed between 1100 and 1900 K

Abstract

The affect of annealing polycrystalline chemical vapor deposition (CVD) diamond in vacuo up to 1900 K has been studied using electron paramagnetic resonance (EPR) and infrared absorption. The concentration of the EPR centers at $g=2.0028\mathrm{}$ and the infrared absorption in the CH region are insensitive to annealing below 1500 K. On annealing at 1700 K it was found that (a) some of the hydrogen on internal grain boundaries or in intergranular material became mobile (in samples with strong CH absorption there was a decrease in the peak at 2920 cm${}^{-1}$ and an increase in the peak at 2820 cm${}^{-1})$ but was not lost from the sample and (b) the intensity of the EPR absorption at $g=2.0028\mathrm{}$ decreased. More than one defect contributes to the EPR absorption at $g=2.0028\mathrm{}$ in the samples studied. Annealing at 1900 K (no graphitization of the external surfaces occurred), in all except one case, severely degraded the optical properties of the samples and a different EPR defect at $g=2.0035\mathrm{}\left(2\right)\mathrm{}$ was created. Infrared measurements showed that hydrogen is lost from most CVD diamond samples when annealed to 1900 K for 4 h.