Surface core-level shifts of strontium observed in photoemission of barium strontium titanate thin films

Angle resolved x-ray photoelectron spectroscopy was used to investigate the surface electronic structure of barium strontium titanate (BST) films. In contrast to previous photoemission studies which identified two chemical states associated with only Ba in the near surface region, the authors have resolved core-level features from surface Sr atoms which provide new insight into the surface electronic structure of BST thin films. The surface Sr 3d features are found to lie approximately 1eV higher in binding energy than the bulk derived peaks. The effects of aqueous and annealing surface treatments and the origin of the Sr surface core-level shifts are discussed.