The defined adsorption site of sodium on the TiO2(110)-(1 x 1) surface

The adsorption site of sodium on the TiO2 (100)-(1 x 1) surface was studied by extended X-ray absorption fine structure. For coverage ranging between 0.25 and 0.5 ML, we find that sodium is on an 'in-between' site where it is bound to two bridging oxygen atoms at 2.25 Angstrom and one in-plane oxygen atom at 2.40 Angstrom, in full agreement with DFT calculations. At higher coverage the site becomes an hollow site where the sodium atom is equidistant to the three oxygen atoms at 2.30 Angstrom, while metallic sodium clusters are also formed at the surface. (C) 2004 Elsevier B.V. All rights reserved.