An interfacial defect layer observed at (Ba,Sr)TiO₃/Pt interface

Barium strontium titanate (Ba,Sr)TiO₃ (BST) thin-films on Pt-substrates were studied by transmission electron microscopy. The films show a columnar structure with the grains of 10-50 nm in diameter. These are oriented parallel to the [001] direction which in turn is parallel to the film growth direction. No amorphous intergrain regions occur. The high-resolution lattice fringe pictures show for the first time that over horizontally extended areas of the interface the lattice of the BST film is modified by the introduction of a defect layer. This observation is discussed in terms of a structural origin of the so-called dead-layer effect responsible for a reduction of the film permittivity with decreasing foil thickness.