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 (l) over bar 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 Kalpha radiation from an X-ray tube feasible. The DeltaI/I values of a number of reflections from the 20 and 50 nm films were measured using synchrotron radiation. The observed DeltaI/I values were in good agreement with the intensity changes expected for polarization switching in the bulk.