First-principles investigation of H2O on HfO2 (1 1 0) surface

As the water to be an important precursor mater in atomic layer deposition (ALD) of preparation of HfO2 thin film, water-gas shift (WGS) reaction and heterogeneous catalysis, surface hydroxyl groups played a vital role as the reactive species that remain on the surface. First-principle calculation based on density functional (DFT) approach and generalized gradient approximation (GGA) have been utilized to investigate the molecular and dissociative adsorption of water molecule on the stoichiometric cubic HfO2 (1 1 0) surface with different sites at different coverages. The calculation employed slab geometry and periodic boundary condition with partial relaxation of atom position. Adsorption geometries, Mulliken population charges and density of states for HfO2single bondH2O, HfO2single bondOH, HfO2single bondO and HfO2single bondH at the coverage of 0.5 ML were also calculated. It was found that the adsorption energies varied a little as coverages increased, and the most favorable configuration of H2O on HfO2 surface was corresponding to the coordination of H2O via its oxygen with the surface (surface Hf atom). It was also confirmed that the coordination interaction and hydrogen bonding were the main contributions in dissociative adsorption process. For both molecular and dissociative adsorption, it has been elucidated that the surface hafnium played a key role as the active site. For dissociation reaction H2O (ads) → H (ads) + OH (ads), the barrier energy calculated to be 17.3 kJ/mol, whereas, the second step dehydrogenation reaction OH (ads) + H (ads) → O (ads) + 2H (ads), hardly occurred on this surface because of the high barrier energy 208.3 kJ/mol.