BaTiO3is a technologically relevant material in the perovskite oxide class with above‐room‐temperature ferroelectricity and a very large electro‐optical coefficient, making it highly suitable for emerging electronic and photonic devices. An easy, robust, straightforward, and scalable growth method is required to synthesize epitaxial BaTiO3thin films with sufficient control over the film's stoichiometry to achieve reproducible thin film properties. Here the growth of BaTiO3thin films by hybrid molecular beam epitaxy is reported. A self‐regulated growth window is identified using complementary information obtained from reflection high energy electron diffraction, the intrinsic film lattice parameter, film surface morphology, and scanning transmission electron microscopy. Subsequent optical characterization of the BaTiO3films by spectroscopic ellipsometry revealed refractive index and extinction coefficient values closely resembling those of stoichiometric bulk BaTiO3crystals for films grown inside the growth window. Even in the absence of a lattice parameter change of BaTiO3thin films, degradation of optical properties is observed, accompanied by the appearance of a wide optical absorption peak in the IR spectrum, attributed to optical transitions involving defect states present. Therefore, the optical properties of BaTiO3can be utilized as a much finer and more straightforward probe to determine the stoichiometry level present in BaTiO3films.
Diffraction analysis in four-dimensional scanning transmission electron microscopy now enables the mapping of local structures including symmetry, strain, and polarization of materials. However, measuring the distribution of these configurations at the unit cell level remains a challenge because most analysis methods require the diffraction disks to be separated, limiting the electron probe sizes to be larger than a unit cell. Here, we show improved spatial resolution in mapping the polarization displacement and phases of BaTiO3sampled at a rate equivalent to the size of the projected unit cells using 4D-STEM. This improvement in spatial resolution is accomplished by masking out the overlapping regions in partially overlapped convergent beam electron diffraction patterns. By reducing the probe size to the order of single projected unit cells in size, the measurement shows local fluctuation within the nanosized rhombohedral domains in tetragonal phased BaTiO3, indicating the origin of phase transition and evolution across different length scales.
more » « less- Award ID(s):
- 1633587
- PAR ID:
- 10363962
- Publisher / Repository:
- American Vacuum Society
- Date Published:
- Journal Name:
- Journal of Vacuum Science & Technology A
- Volume:
- 40
- Issue:
- 1
- ISSN:
- 0734-2101
- Page Range / eLocation ID:
- Article No. 013205
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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