J. Phys. Chem. C 2010, 114, 11157–11161
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Water Adsorption on ZnO(0001): Transition from Triangular Surface Structures to a Disordered Hydroxyl Terminated phase ¨ nsten,* Dunja Stoltz, Pål Palmgren, Shun Yu, Mats Go¨thelid, and Ulf O. Karlsson Anneli O Materials Physics, Royal Institute of Technology KTH, Isafjordsgatan 22, S-164 40 Kista, Sweden ReceiVed: January 18, 2010; ReVised Manuscript ReceiVed: April 29, 2010
We present room temperature scanning tunneling microscopy and photoemission spectroscopy studies of water adsorption on the Zn-terminated ZnO(0001) surface. Data indicates that the initial adsorption is dissociative leaving hydroxyl groups on the surface. At low water coverage, the adsorption occurs next to the oxygen-terminated step edges, where water is believed to bind to zinc cations leaving off hydrogen atoms to under-coordinated oxygen anions. When increasing the water dose, triangular terraces grow in size and pits diminish until the surface is covered with wide irregular terraces and a large number of small pits. Higher water exposure (20 Langmuir) results in a much more irregular surface. Hydrogen, which is produced in the dissociation reaction is believed to have an important role in the changed surface structure at high exposures. The fact that adsorbed water completely changes the structure of ZnO(0001) is an important finding toward the understanding of this surface at atmospheric conditions. Introduction Interaction between water and metal oxides is important in fields as catalysis, corrosion, and geology. At normal air pressures, most metal surfaces are oxidized and all surfaces are covered with a water layer, whose thickness depends on the relative humidity of the air.1 Even at ultrahigh vacuum (UHV) conditions (
