Sensitivity of synchrotron radiation x-ray diffraction to the chemical ordering in epitaxial perovskite multilayers
Résumé
The present work shows that the chemical ordering in (BaTiO3/SrTiO3)(N) chemical-vapor-deposition-grown superlattices can be reliably estimated by synchrotron radiation x-ray diffraction (XRD). XRD (00l) diagrams for l=1-8 have been simultaneously simulated using a unique set of parameters describing the stack with a model based on periodic structural and chemical profiles. The relative sensitivity of the (00l) reflections to the atomic concentrations of Sr and Ba is presented: the SrTiO3 and BaTiO3 scattering factors partially compensate each other for the l odd, and their respective contributions in the (007) reflection can be disentangled. Using this property, an accuracy as good as 5% can be obtained regarding the Ba and Sr atomic concentrations. Synchrotron radiation reflectivity was performed, and the simulation confirms the observed large atomic interlayer diffusion. Moreover, energy electron loss spectroscopy measurements at the barium and the strontium edges give a very good agreement with the diffusion profiles determined from our XRD diagram simulations. In such oxide multilayers, the extracted chemical profile does not fully obey Vegard's law.