Water adsorption on diamond (111) surfaces: an ab initio study

The physical and chemical adsorption of water at the (1 × 1) and (2 × 1)-reconstructed C(111) surfaces are investigated by means of first principles calculations and compared to hydrogen adsorption. The study aims at filling a gap of knowledge about the interaction of water with the most stable diamond surface. The calculated reaction energies and barriers indicate that the Pandey-reconstructed surface is almost inert towards water and hydrogen chemisorption in comparison with the unreconstructed surface and other low-index diamond surfaces. We also show that by increasing the amount of chemisorbed hydroxyl or hydrogen groups the stability of the Pandey reconstruction is progressively reduced with respect to the unreconstructed (111) surface, which becomes energetically more favourable above about 40% of adsorbate coverage. Our results provide a microscopic description of diamond surface passivation, which is very important for controlling macroscale phenomena, such as the friction reduction of diamond coatings in humid environments.