Real-time X-ray study of roughness scaling in the initial growth of epitaxial BaTiO3/LaNiO3 superlattices

The evolution of surface and interface roughness during heteroepitaxial growth of strained BaTiO3/LaNiO3(BTO/LNO) superlattices on SrTiO3 (0 0 1) substrates was investigated using real-time X-ray reflectivity measurements in situ with synchrotron radiation. The roughness scaling of the growth front and interface of superlattices with modulation length below (2 and 6 nm) and beyond (20 nm) the critical thickness was studied against the bilayer number. The fitted results of in situ specular X-ray reflectivity curves reveal a two-dimensional growth of BTO and LNO sublayers on the SrTiO3 substrate for superlattices with a modulation length below the critical thickness. Moreover, a larger root-mean-square roughness of BTO/LNO interface was obtained in the superlattice with modulation length beyond the critical thickness indicating lattice relaxation in the superlattice structure. Fitted results of in situ specular X-ray reflectivity curves provide the first evidence for power-law scaling of the root-mean-square roughness of an interface and a surface in the superlattice structure. Observation of such a roughness scaling behavior indicates that strain plays an important role in the determination of microstructure in the growth of epitaxial BTO/LNO superlattices.