Polarization switching in BaTiO₃ thin films measured by X-ray diffraction exploiting anomalous dispersion

Films of BaTiO₃ ranging from 20 nm to 300 nm in thickness were grown with pulsed laser deposition on Nb:SrTiO₃. The quality of the layers was investigated using atomic force microscopy, X-ray reflectivity and X-ray diffraction. Both the micrographs and the X-ray reflectivity spectra indicate a smooth surface of the layers. The X-ray diffraction profiles measured using synchrotron radiation show features characteristic for highly crystalline thin films. The application of an external electric field parallel to the c axis changes an hkl reflection of BaTiO₃ to an hk reflection. Due to the anomalous dispersion, the intensities of these two reflections are not equal and the atomic displacements can be determined from the intensity differences. The electric field-induced intensity changes can be as large as a few percent, which makes data collection from a 100 nm film using Cu Kα radiation from an X-ray tube feasible. The ΔI/I values of a number of reflections from the 20 and 50 nm films were measured using synchrotron radiation. The observed ΔI/I values were in good agreement with the intensity changes expected for polarization switching in the bulk.