Electronic Structure of Epitaxial Sn-Doped Anatase Grown on SrTiO3(001) by Dip Coating

Sn doping in the anatase polymorph of TiO2 promotes transformation to the thermodynamically stable rutile phase at much lower temperature than found for the undoped material. Here it is shown that the anatase-to-rutile phase transition in Sn-doped TiO2 is inhibited in epitaxial (001) oriented films grown on SrTiO3(001) by a dip coating procedure. X-ray photoemission spectroscopy demonstrates that there is pronounced segregation of Sn to the anatase (001) surface and that the bandgap increases with Sn doping level. This behavior is in contrast to that found in the rutile phase of Sn-doped TiO2, where the bandgap initially decreases for low levels of Sn doping. Pure SnO2 cannot be stabilized by epitaxy in the anatase phase even though good matching between anatase SnO2(001) and SrTiO3(001) is predicted by density functional theory calculations.