Structural and Compositional Effects in Epitaxially-Strained Vanadate Thin Films

Breaking the inversion symmetry in artificial hetero-structures is proving to be a powerful approach to create novel quantum states, thereby providing new functionalities with potential for the development of revolutionary devices. Based on this, a way to achieve “hybrid improper ferroelectricity” in perovskite superlattices was recently devised by ab - initio theory [1, 2]. The working principle rests on the stacking of odd numbers of orthorhombic distorted AB O 3 and A ’ B O 3 unit cells in order to generate a macroscopic polarization out of the uncompensated displacements of the A site cations in the superlattice. These displacements are the result of the strong coupling between chemistry and structure in perovskite oxides. Towards this goal, here we investigate A VO 3 epitaxial thin films grown under different conditions by pulsed laser deposition, where A is either La or Pr, using aberration-corrected scanning transmission electron microscopy (STEM) to identify local strain-induced structural and compositional effects. The films are studied using a double aberration-corrected Titan Themis 60-300 operated at 300 kV, using a 20 mrad convergence semi-angle. High angle annular dark field (HAADF) and annular bright field (ABF) image series are simultaneously recorded, typically at consecutive scans rotations of 90 ° , using Fischione and Gatan photomuliplier tube detectors respectively. Post-acquisition, effects of scan drift and other distortions are compensated via rigid and non-rigid alignment using Smart Align [3]. Chemical analyses are made with energy dispersive X-ray spectroscopy, using ChemiSTEM detectors and Velox software, and electron energy-loss