Growth of stoichiometric LaTiO₃ thin films by pulsed laser deposition

Oxide heterostructures exhibit fascinating properties, e.g., the coexistence of superconductivity and ferromagnetism at the interface of LaAlO₃/SrTiO₃, but the extraordinary electronic properties of transition metal oxides (TMOs) caused by electron correlation yet wait to be fully harnessed. The Mott insulator LaTi³⁺O₃ (LTO) is a prototypical material for such strongly correlated TMOs, which can be prepared by pulsed laser deposition. However, in order to obtain stoichiometric LTO strongly reducing growth conditions are required since the thermodynamically stable bulk phase is the oxygen-rich band insulator La₂Ti⁴⁺₂O₇. We therefore systematically study the impact of oxidizing and reducing background atmospheres and the oxygen out diffusion from the substrate into thin LTO films. In situ x-ray photoelectron spectroscopy of films prepared on STO reveals overoxidation due to oxygen out-diffusion from the STO substrate, which can be partially suppressed by introducing a LaAlO_3-x (LAO) buffer layer. Further control over the oxygen stoichiometry is gained by the use of DyScO₃ substrates, presumably due to the lower mobility of oxygen. Overoxidation during storage in air can be prevented by introducing a LAO capping layer of a few unit cells thickness, acting again as a diffusion barrier for oxygen.