Structural characteristics of epitaxial BaTiO3/LaNiO3 superlattice

Artificial superlattices consisting of ferroelectric BaTiO3 (BTO) and conductive LaNiO3 (LNO) sublayers were epitaxially grown on Nb-doped SrTiO3(001) single crystal substrates by a dual-gun rf magnetron sputtering system. A symmetric sublayer structure with the designed thickness varying in the range from 3 nm to 70 nm was adopted. The formation of superlattice structure was confirmed from the (00L) Bragg reflection of x ray and the depth profile of secondary ion mass spectrometry. The in-plane diffraction shows that the BTO and LNO sublayers have the same in-plane lattice spacing for the superlattices with stacking periodicity below 16 nm. The lattice parameter obtained from in-plane diffraction also exhibits a partial but nearly constant relaxation of in-plane strain in the superlattices, even though the sublayer thickness is below the critical value for generation of misfit dislocations. X-ray reflectivity measurement reveals that all the above superlattices have about the same interface roughness of BTO/LNO. Consequently, nearly the same extent of dielectric enhancement results from the strained BTO layer, along with a highly conductive interface zone in the superlattiecs.