Extracting the near surface stoichiometry of BiFe0.5Mn0.5O3 thin films; a finite element maximum entropy approach

The surface and near-surface chemical composition of BiFe0.5Mn0.5O3 has been studied using a combination of low photon energy synchrotron photoemission spectroscopy, and a newly developed maximum entropy finite element model from which it is possible to extract the depth dependent chemical composition. In the uppermost few unit cells, an overabundance of Bi, and a deficiency of Fe and Mn are observed. In deeper layers, the measurements are consistent with bulk-like stoichiometry. Additionally, a definitive identification of all the observed species together with their abundance and depth dependence is given, and the mixed Fe and Mn valencies are estimated. In addition to the expected bulk valencies Mn3+ and Fe3+, some Fe2+ and a small amount of Mn4+ are also observed. The maximum entropy finite element model demonstrated here is also discussed in more general terms and its potential application to the broader field of perovskite thin films is made apparent. (C) 2012 Elsevier B.V. All rights reserved.