Stability of diamond-like carbon in hydrothermal conditions

摘要

The effect of water at high temperature and pressure (hydrothermal conditions) in a tetrahedral amorphous carbon (ta-C) type of diamond-like carbon has been investigated. At temperatures over 200 deg C, the action of water leads to the sp~3 to sp~2 conversion in diamond-like carbon rich in sp~3 bonds and the almost complete transformation into sp~2 bonded amorphous carbon (a-C) at temperatures below 600 deg C. After treatment at 600 deg C, open porous structures of interconnected multiwall cells were observed. The formation of curved graphitic shells is explained by the partial etching/dissolution of the carbon film and precipitation from the reactive hydrothermal fluid. The high ratio of sp~3 carbon nuclei present does not seem to promote the precipitation of additional sp~3-bonded carbon from the supercritical fluid, rather the growth of crystalline multiwall graphitic layers with sp~2-bonding, as demonstrated with micro and macro-Raman measurements.