The surface stress of the (1 1 0) and (1 0 0) surfaces of rutile and the effect of water adsorbents

The surface stress on clean TiO2 (1 1 0) and (1 0 0) surfaces, and those with four types of adsorbent – (i) molecularly adsorbed water, (ii) dissociatively adsorbed water, (iii) dissociatively adsorbed water at an oxygen vacancy, and (iv) adsorbed hydrogen – was investigated in the framework of density functional theory using a slab model. The calculations were intended to rationalize the effect of the artificially introduced stress that occurs in experimentally photoinduced hydrophilicity. Tensile stress was observed for a clean (1 1 0) surface, and a mixture of tensile and compressive stress for a clean (1 0 0) surface. The adsorbate-induced surface stresses were analyzed in terms of the sixfold coordinated character of the surface titanium atoms, hydrogen bonds between the adsorbents and the bridging oxygen atoms, and the change in electron density in the vicinity of the surface.