Direct observation of a fully strained dead layer at $Ba0.7Sr0.3TiO3∕SrRuO3$ interface

Epitaxial $SrRuO3∕Ba0.7Sr0.3TiO3$ (BST)/$SrRuO3$ thin film capacitors were prepared on $SrTiO3$ substrates by pulsed laser deposition. The structures of stacked BST films with different thicknesses were investigated by transmission electron microscopy. A distinctive layer of about $3nm$ of thickness was identified within BST films thicker than $9nm$ at the interface with the $SrRuO3$ bottom electrode. The distinctive layer is misfit dislocation-free showing pseudoconstant lattice parameters. Misfit dislocations are formed at the interface between the distinctive layer and the BST film bulk layer relaxing the latter as the film thickness increases. The effect of the distinctive layer on the system dielectric response is discussed within the framework of an interfacial dead-layer model.