Stabilization of the Perovskite Phase in the Y–Bi–O System By Using a BaBiO₃ Buffer Layer

Abstract

A topological insulating phase has theoretically been predicted for the thermodynamically unstable perovskite phase of YBiO 3 . Here, it is shown that the crystal structure of the Y-Bi-O system can be controlled by using a BaBiO 3 buffer layer. The BaBiO 3 film overcomes the large lattice mismatch of 12% with the SrTiO 3 substrate by forming a rocksalt structure in between the two perovskite structures. Depositing an YBiO 3 film directly on a SrTiO 3 substrate gives a fluorite structure. However, when the Y-Bi-O system is deposited on top of the buffer layer with the correct crystal phase and comparable lattice constant, a single oriented perovskite structure with the expected lattice constants is observed.Topological materials are at the focus of a relatively young field in material science, aiming to find both new topological materials as well as discovering novel applications for this new class of matter. The most prominent phenomena that emerge in topological materials include a chiral spin structure and topologically protected surface states. [1,2] The spin-momentum locking makes topological matter interesting for spintronic applications [1,3,4] and possibly quantum computation. [5] Therefore, global research is conducted towards further developing known topological materials and trying to find new compounds that have a non-trivial topology in their band structure.So far, only a handful of materials have been identified as topological insulators (TIs). Within a year after the theoretical prediction of Bernevig et al., [1] König et al. [3] observed the quantum spin Hall state in CdTe/HgTe/CdTe quantum wells À the first system known with a non-trivial band structure. Bi 1-x Sb x was the first three-dimensional TI that was experimentally observed, [6] followed by Bi 2 Se 3 , [7] and Bi 2 Te 3 . [4] The relatively heavy bismuth gives rise to strong spin-orbit coupling (SOC) effects, which in turn results in a band inversion at an odd

Atomic‐Scale Interface Structure in Domain Matching Epitaxial BaBiO3 Thin Films Grown on SrTiO3 Substrates

“…This can be clearly seen in the image of Figure , where the interface layer changes from 3 (left) to 2 (right) Bi layers, as evaluated on the basis of the lattice coherency at both the BBO/BO and BO/STO interfaces (see also the positions of the MDs marked by “T”). Similar observations were also reported in the study by Bouwmeester et al, however, no direct evidences were provided. By controlling the thickness variations of the interface layer (e.g., by deliberately depositing a BO‐like layer prior to the BBO growth), the film quality may be further improved.…”

“…This is evident from the comparison with the corresponding projections of δ ‐Bi 2 O 3 , as shown in Figure c,d, which match our findings almost perfectly. Inconsistent with a recent report, the interfacial layer was reported to possess a rock‐salt structure based on the HAADF image alone. The orientation relationship between the interface BO‐like layer and surrounding perovskites (i.e., STO and BBO) is found to be <001> BO ||<001> P and <110> BO ||<100> P .…”

“…Although it was experimentally found that a wetting layer with thickness of about 1 nm might exist at the interface, information on the detailed microstructures for such a layer and their role in the subsequent film growth is lacking, particularly at the atomic scale. For example, using high‐angle annular dark‐field (HAADF) scanning transmission electron microscopy (STEM) imaging, this interfacial layer was reported to possess a rock‐salt structure, whose formation can decouple the substrate from the film, thus stabilizing the heterostructure . However, it should be noted that the determination of the oxygen positions is of critical importance in distinguishing fluorites from rock salts, as both structures appear the same in the HAADF images (oxygen is invisible).…”

“…For example, using high‐angle annular dark‐field (HAADF) scanning transmission electron microscopy (STEM) imaging, this interfacial layer was reported to possess a rock‐salt structure, whose formation can decouple the substrate from the film, thus stabilizing the heterostructure . However, it should be noted that the determination of the oxygen positions is of critical importance in distinguishing fluorites from rock salts, as both structures appear the same in the HAADF images (oxygen is invisible). So far, this distinction has not been achieved.…”

Simultaneous heteroepitaxial growth of SrO (001) and SrO (111) during strontium-assisted deoxidation of the Si (001) surface

“…Within the glove box, the sample was placed into a Kammrath & Weiss GmbH transfer module which possesses a one way valve that does not allow the inow of gas from the outside, together with the Omniprobe copper support grid and then transferred to the FIB (FEI Helios 650). [50][51][52][53][54][55] The FIB sample was prepared as described elsewhere 56 and transferred without exposure to air into a Gatan double-tilt vacuum transfer holder for TEM investigation using a FEI Titan 60-300 microscope with an X-FEG high brightness electron source, a probe Cs corrector, a Super-X 4-quadrant EDX detector and a Gatan GIF Ennium electron energy loss (EEL) spectrometer. The microscope was operated in scanning TEM mode at 120 kV and 10 pA to minimize damage to the lm.…”