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  1. Free, publicly-accessible full text available June 1, 2023
  2. Abstract Multiferroic materials have generated great interest due to their potential as functional device materials. Nanocomposites have been increasingly used to design and generate new functionalities by pairing dissimilar ferroic materials, though the combination often introduces new complexity and challenges unforeseeable in single-phase counterparts. The recently developed approaches to fabricate 3D super-nanocomposites (3D‐sNC) open new avenues to control and enhance functional properties. In this work, we developed a new 3D‐sNC with CoFe2O4 (CFO) short nanopillar arrays embedded in BaTiO3 (BTO) film matrix via microstructure engineering by alternatively depositing BTO:CFO vertically-aligned nanocomposite layers and single-phase BTO layers. This microstructure engineering methodmore »allows encapsulating the relative conducting CFO phase by the insulating BTO phase, which suppress the leakage current and enhance the polarization. Our results have demonstrated that microstructure engineering in 3D‐sNC offers a new bottom–up method of fabricating advanced nanostructures with a wide range of possible configurations for applications where the functional properties need to be systematically modified.« less
    Free, publicly-accessible full text available May 2, 2023
  3. We report the dielectric Properties of HfO 2 -based films in the optical–high frequency range. The demonstrated tunability of the optical dielectric constant of HfO 2 -based compounds is of great relevance for optoelectronic applications, e.g., high-refractive index dielectrics for nanoantenna and optical coatings for electronic displays. Since the optical dielectric constant of HfO 2 is determined by the electronic structure and its crystal environment, we tune the physical properties of HfO 2 films on MgO by adding different dopants. In this work, we aim to determine the influence of doping together with the resulting crystal structure on the opticalmore »dielectric constant. Hence, we studied 20 mol. % Y-doped HfO 2 (HYO), Hf 0.5 Zr 0.5 O 2 (HZO), and Hf 0.5 Ce 0.5 O 2 (HCO). Among the dopants, Y 2 O 3 has the lowest, ZrO 2 an intermediate, and CeO 2 the highest real part of the optical dielectric constant. The optical dielectric constant is found to be lowest in the cubic HYO films. An intermediate dielectric constant is found in HZO films that is predominantly in the monoclinic phase, but additionally hosts the cubic phase. The highest dielectric constant is observed in HCO films that are predominantly in the cubic phase with inclusions of the monoclinic phase. The observed trend is in good agreement with the dominant role of the dopant type in setting the optical dielectric constant.« less
    Free, publicly-accessible full text available May 1, 2023
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  5. Free, publicly-accessible full text available April 1, 2023
  6. Free, publicly-accessible full text available March 1, 2023
  7. Perovskite offers a framework that boasts various functionalities and physical properties of interest such as ferroelectricity, magnetic orderings, multiferroicity, superconductivity, semiconductor, and optoelectronic properties owing to their rich compositional diversity. These properties are also uniquely tied to their crystal distortion which is directly affected by lattice strain. Therefore, many important properties of perovskite can be further tuned through strain engineering which can be accomplished by chemical doping or simply element substitution, interface engineering in epitaxial thin films, and special architectures such as nanocomposites. In this review, we focus on and highlight the structure–property relationships of perovskite metal oxide films andmore »elucidate the principles to manipulate the functionalities through different modalities of strain engineering approaches.« less
    Free, publicly-accessible full text available March 1, 2023
  8. Free, publicly-accessible full text available December 28, 2022
  9. Here, in ionically conducting Na 0.5 Bi 0.5 TiO 3 (NBT), we explore the link between growth parameters, stoichiometry and resistive switching behavior and show NBT to be a highly tunable system. We show that the combination of oxygen ionic vacancies and low-level electronic conduction is important for controlling Schottky barrier interfacial switching. We achieve a large ON/OFF ratio for high resistance/low resistance ( R HRS / R LRS ), enabled by an almost constant R HRS of ∼10 9 Ω, and composition-tunable R LRS value modulated by growth temperature. R HRS / R LRS ratios of up to 10more »4 and pronounced resistive switching at low voltages (SET voltage of <1.2 V without high-voltage electroforming), strong endurance (no change in resistance states after several 10 3 cycles), uniformity, stable switching and fast switching speed are achieved. Of particular interest is that the best performance is achieved at the lowest growth temperature studied (600 °C), which is opposite to the case of most other perovskite oxides for memristors, where higher growth temperatures are required for optimum performance. This is understood based on the oxygen vacancy control of interfacial switching in NBT, whereas a range of other mechanisms (including filamentary switching) occur in other perovskites. The study of NBT has enabled us to determine key parameters for achieving high performance memristors.« less