Abstract
Ferroelectric thin films grown on high index substrates show unusual structural and switching dynamics due to their special strain states. Understanding the misfit relaxation behavior is crucial to facilitate the high index thin film growth with improved quality. In this paper, ferroelectric PbTiO3 thin films were grown on LaAlO3 (111) substrates by pulsed laser deposition technique. The microstructures were investigated by combinations of conventional and aberration-corrected transmission electron microscopy. Diffraction contrast analysis and high resolution imaging reveal that high density interfacial dislocations were distributed at the interfaces. These dislocations have mixed character with Burgers vectors of a <110> and line directions of <112>. The edge components of the dislocations, with the Burgers vectors parallel to the interface, accommodate the lattice mismatch and are the main contributor to the misfit relaxation of this system. The formation mechanism of these dislocations is proposed and discussed to elucidate the novel mismatch relaxation behavior of <111> oriented perovskite films.
Highlights
High-index ABO3 perovskite oxide thin films have attracted much attention recently because of their unusual characteristics in contrast to conventional low-index ABO3 films1,2
High index surfaces involving polar discontinuities tend to increase surface energies for ABO3 perovskite oxides in general which will be an enormous challenge for the growth of epitaxial high-index ABO3 films9
It is well known that bulk LAO is rhombohedral with the lattice parameters of arh = 5.63 Å and space group of R-3c at room temperature17
Summary
High-index ABO3 perovskite oxide thin films have attracted much attention recently because of their unusual characteristics in contrast to conventional low-index ABO3 films. High index surfaces involving polar discontinuities tend to increase surface energies for ABO3 perovskite oxides in general which will be an enormous challenge for the growth of epitaxial high-index ABO3 films9 Such polar discontinuity has a huge electrostatic energy cost and triggers a series of screening mechanisms that yield the accumulation of free charge at the interface. Transmission electron microscopy (TEM) and aberration-corrected scanning transmission electron microscopy (STEM), which could provide resolution to the sub-angstrom level and identify different atom columns directly, were used for investigating interfacial structures and strain/defects in PTO (111) films15,16 These films were grown epitaxially on LaAlO3 (111) (LAO (111)) substrates by pulsed laser deposition (PLD) technique. The formation mechanism of these novel misfit dislocations is proposed and discussed as well
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