Atomic-Scale Interface Structure in Domain Matching Epitaxial BaBiO3 Thin Films Grown on SrTiO3 Substrates

The electronic structures of BaBiO3 (BBO) thin films grown on SrTiO3 substrates are found to be thickness dependent. The origin of this behavior remains under debate and has been suggested to be attributed to the structural and compositional modifications at the BBO/SrTiO3 interface during the first stage of film growth. Though a wetting layer with thickness of approximate to 1 nm has been experimentally identified at the interface, details on the microstructures of such a layer and their effect on the subsequent film growth are lacking so far, particularly at the atomic scale. Herein, atomic-resolution scanning transmission electron microscopy is used to study the interface structure of a 30 nm-thick BBO film grown on an Nb-doped SrTiO3 (STO) substrate through domain matching epitaxy. An interfacial delta-Bi2O3 (BO)-like phase with fluorite structure is identified, showing a layer-by-layer spacing of approximate to 3.2 angstrom along the growth direction. The orientation relationship between the BO-like phase and surrounding perovskites (P) is found to be (BO)||(P) and (BO)||(P). The presence of the BO-like phase results in two types of interfaces, i.e., a coherent BO/STO and a semicoherent BBO/BO interface. Thickness variations are observed in the BO-like layer, resulting in the formation of antiphase domains in the BBO films.