Interaction of diamond with water: an in situ XANES investigation

The interaction of water and oxygen with a polycrystalline diamond film was investigated using XANES (X-ray absorption near edge structure) spectroscopy. A novel reactor design allowed to access pressure ranges up to 4.0 mbar and simultaneous recording of the gas phase and sample spectra at the C K- and O K-edges, respectively. The diamond surface is inert with respect to the interaction with water in the investigated temperature below 500°C. A defect (sp2 carbon) -rich surface layer, is created through ion irradiation (Ar+, 2 keV), and the ratio of the π∗/σ∗ resonance was used as a measure of the extent of damage. A partial removal of the damage is observed in the first few minutes of water exposure, but a steady-state concentration of defects remains even after prolonged exposure periods. The resultant steady-state damage is nearly independent of the water pressure. The reaction of the damaged surface with water leads also to the attachment of oxidic groups, mostly in the form of carbonyl groups, to the surface. The carbonyl groups seem to be located mostly at the surface and result directly from the reaction with dangling bonds or sp2 carbon defects with water. The irradiation with oxygen ions leads likewise to an overall reduction in damage, the chemical etching dominates the creation of new defects through ion impact.