Crystallographic and microstructural studies of BaTiO₃ thin films grown on SrTiO₃ by laser molecular beam epitaxy

A series of trial tests were carried out to grow BaTiO₃ thin films on SrTiO₃ substrates in our newly built laser molecular beam epitaxial system. The phase, crystallographic orientation and crystalline quality of the films were investigated by x-ray diffraction $θ$/2$θ$ scan, symmetric and asymmetric rocking curves $(ω$ scans) and φ scan. The interfacial microstructures of the BaTiO₃/SrTiO₃ and the surface morphology of BaTiO₃ films were analyzed by cross-section transmission electron microscopy and atomic force microscopy. Under appropriate growth conditions, epitaxial, single-crystal films with fully c-axis oriented tetragonal structure were obtained. The tetragonality was calculated by using {303} asymmetric rocking curve for a BaTiO₃ thin film to be 1.027, which is larger than the bulk value of BaTiO₃. The BaTiO₃/SrTiO₃ interface is very abrupt with no transitional layer and the BaTiO₃ film exhibits an atomically smooth surface.