skip to main content


Title: Molecular beam epitaxy of KTaO3
Strain-engineering is a powerful means to tune the polar, structural, and electronic instabilities of incipient ferroelectrics. KTaO3 is near a polar instability and shows anisotropic superconductivity in electron-doped samples. Here, we demonstrate growth of high-quality KTaO3 thin films by molecular-beam epitaxy. Tantalum was provided by either a suboxide source emanating a TaO2 flux from Ta2O5 contained in a conventional effusion cell or an electron-beam-heated tantalum source. Excess potassium and a combination of ozone and oxygen (10% O3 + 90% O2) were simultaneously supplied with the TaO2 (or tantalum) molecular beams to grow the KTaO3 films. Laue fringes suggest that the films are smooth with an abrupt film/substrate interface. Cross-sectional scanning transmission electron microscopy does not show any extended defects and confirms that the films have an atomically abrupt interface with the substrate. Atomic force microscopy reveals atomic steps at the surface of the grown films. Reciprocal space mapping demonstrates that the films, when sufficiently thin, are coherently strained to the SrTiO3 (001) and GdScO3 (110) substrates.  more » « less
Award ID(s):
2122147
NSF-PAR ID:
10423979
Author(s) / Creator(s):
; ; ; ; ; ; ; ;
Date Published:
Journal Name:
Journal of vacuum science technology A Vacuum surfaces and films
Volume:
41
Issue:
2
ISSN:
0734-2101
Page Range / eLocation ID:
022703
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Strain-engineering is a powerful means to tune the polar, structural, and electronic instabilities of incipient ferroelectrics. KTaO 3 is near a polar instability and shows anisotropic superconductivity in electron-doped samples. Here, we demonstrate growth of high-quality KTaO 3 thin films by molecular-beam epitaxy. Tantalum was provided by either a suboxide source emanating a TaO 2 flux from Ta 2 O 5 contained in a conventional effusion cell or an electron-beam-heated tantalum source. Excess potassium and a combination of ozone and oxygen (10% O 3 + 90% O 2 ) were simultaneously supplied with the TaO 2 (or tantalum) molecular beams to grow the KTaO 3 films. Laue fringes suggest that the films are smooth with an abrupt film/substrate interface. Cross-sectional scanning transmission electron microscopy does not show any extended defects and confirms that the films have an atomically abrupt interface with the substrate. Atomic force microscopy reveals atomic steps at the surface of the grown films. Reciprocal space mapping demonstrates that the films, when sufficiently thin, are coherently strained to the SrTiO 3 (001) and GdScO 3 (110) substrates. 
    more » « less
  2. Hybrid molecular beam epitaxy (MBE) growth of Sn-modified BaTiO3 films was realized with varying domain structures and crystal symmetries across the entire composition space. Macroscopic and microscopic structures and the crystal symmetry of these thin films were determined using a combination of optical second harmonic generation (SHG) polarimetry and scanning transmission electron microscopy (STEM). SHG polarimetry revealed a variation in the global crystal symmetry of the films from tetragonal (P4mm) to cubic (Pm3¯m) across the composition range, x = 0 to 1 in BaTi1−xSnxO3 (BTSO). STEM imaging shows that the long-range polar order observed when the Sn content is low (x = 0.09) transformed to a short-range polar order as the Sn content increased (x = 0.48). Consistent with atomic displacement measurements from STEM, the largest polarization was obtained at the lowest Sn content of x = 0.09 in Sn-modified BaTiO3 as determined by SHG. These results agree with recent bulk ceramic reports and further identify this material system as a potential replacement for Pb-containing relaxor-based thin film devices.

     
    more » « less
  3. 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 BaSnO3films grown on two different perovskite substrates: LaAlO3and PrScO3. These BaSnO3films 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.

     
    more » « less
  4. We report the molecular beam epitaxy of Bi1−xSbx thin films (0 ≤ x ≤ 1) on sapphire (0001) substrates using a thin (Bi,Sb)2Te3 buffer layer. The characterization of the films using reflection high energy diffraction, x-ray diffraction, atomic force microscopy, and scanning transmission electron microscopy reveals the epitaxial growth of films of reasonable structural quality. This is further confirmed via x-ray diffraction pole figures that determine the epitaxial registry between the thin film and the substrate. We further investigate the microscopic structure of thin films via Raman spectroscopy, demonstrating how the vibrational modes vary as the composition changes and discussing the implications for the crystal structure. We also characterize the samples using electrical transport measurements.

     
    more » « less
  5. Abstract

    The making of BaZrS3thin films by molecular beam epitaxy (MBE) is demonstrated. BaZrS3forms in the orthorhombic distorted‐perovskite structure with corner‐sharing ZrS6octahedra. The single‐step MBE process results in films smooth on the atomic scale, with near‐perfect BaZrS3stoichiometry and an atomically sharp interface with the LaAlO3substrate. The films grow epitaxially via two competing growth modes: buffered epitaxy, with a self‐assembled interface layer that relieves the epitaxial strain, and direct epitaxy, with rotated‐cube‐on‐cube growth that accommodates the large lattice constant mismatch between the oxide and the sulfide perovskites. This work sets the stage for developing chalcogenide perovskites as a family of semiconductor alloys with properties that can be tuned with strain and composition in high‐quality epitaxial thin films, as has been long‐established for other systems including Si‐Ge, III‐Vs, and II‐VIs. The methods demonstrated here also represent a revival of gas‐source chalcogenide MBE.

     
    more » « less