Abstract
Detailed microstructure analysis of epitaxial thin films is a vital step towards understanding essential structure-property relationships. Here, a combination of transmission electron microscopy (TEM) techniques is utilized to determine in detail the microstructure of epitaxial La-doped BaSnO3 films grown on two different perovskite substrates: LaAlO3 and PrScO3. These BaSnO3 films are of high current interest due to outstanding electron mobility at ambient. The rotational disorder of low-angle grain boundaries, namely the in-plane twist and out-of-plane tilt, is visualized by conventional TEM under a two-beam condition, and the degree of twists in grains of such films is quantified by selected-area electron diffraction. The investigation of the atomic arrangement near the film-substrate interfaces, using high-resolution annular dark-field scanning TEM imaging, reveals that edge dislocations with a Burgers vector along [001] result in the out-of-plane tilt. It is shown that such TEM-based analyses provide detailed information about the microstructure of the films, which, when combined with complimentary high-resolution X-ray diffraction, yields a complete structural characterization of the films. In particular, stark differences in out-of-plane tilt on the two substrates are shown to result from differences in misfit dislocation densities at the interface, explaining a puzzling observation from X-ray diffraction.
Highlights
Increased interest in BaSnO3 (BSO) has emerged in recent years due to its optical transparency in the visible range and attractive electronic transport properties, including high electron mobility, exceeding 300 cm2V−1s−1, in bulk single crystals at room temperature[1,2,3]
The lattice mismatch between a BSO film and its substrate directly influences the formation of misfit dislocations (MDs) at the interface, but might play some role in determining the density of threading dislocations (TDs), and the grain misorientations, throughout the film[19]
We examine the microstructure of BSO films grown on LaAlO3 (LAO) and PrScO3 (PSO) substrates, with rather different lattice mismatch, using Conventional TEM (CTEM) and annular dark-field-scanning TEM (STEM) (ADF-STEM)
Summary
Received: 14 March 2018 Accepted: 19 June 2018 Published: xx xx xxxx of BaSnO3 thin films on LaAlO3 and PrScO3 substrates from transmission electron microscopy. A combination of transmission electron microscopy (TEM) techniques is utilized to determine in detail the microstructure of epitaxial La-doped BaSnO3 films grown on two different perovskite substrates: LaAlO3 and PrScO3. These BaSnO3 films are of high current interest due to outstanding electron mobility at ambient. The film-substrate interface is further explored using cross-sectional atomic-resolution ADF-STEM imaging These results, in combination with complementary high-resolution XRD, enable us to elucidate the relationship between the microstructure of the films and the interface atomic structure, in particular elaborating the role of MDs in determining the very different out-of-plane tilts on the two substrates
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