Long term oxidation behavior of micro- and nano-crystalline CVD diamond foils

Abstract Nano- and micro-crystalline diamond foils with a thickness of at least 30 μm are manufactured by hot-filament chemical vapor deposition (HFCVD) in an industrial coating machine. Some of them are doped with trimethylborate. The diamond foils are exposed to air at 450 °C and 500 °C and oxidized for up to 738 h. At these temperatures all investigated diamond foils exhibit a substantial weight loss, which is measured with a high precision balance. Nanocrystalline diamond foils show a high weight loss rate compared to microcrystalline diamond foils. At 500 °C the weight loss rate is two to seven times higher than that at 450 °C. Grain boundaries and small diamond crystals are etched much faster than larger diamond crystal. The incorporation of boron does not significantly affect the oxidation of the diamond foils.