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  1. 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 develop 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 method allows encapsulating the relative conducting CFO phase by the insulating BTO phase, which suppress the leakage current and enhance the polarization. Our results demonstrate 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.

  2. 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 optical 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 predominantlymore »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
  3. Free, publicly-accessible full text available June 1, 2023
  4. 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 and elucidate the principles to manipulate the functionalities through different modalities of strain engineering approaches.
    Free, publicly-accessible full text available March 1, 2023
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  6. Free, publicly-accessible full text available April 1, 2023
  7. Free, publicly-accessible full text available December 28, 2022
  8. Abstract The convergence of proton conduction and multiferroics is generating a compelling opportunity to achieve strong magnetoelectric coupling and magneto-ionics, offering a versatile platform to realize molecular magnetoelectrics. Here we describe machine learning coupled with additive manufacturing to accelerate the design strategy for hydrogen-bonded multiferroic macromolecules accompanied by strong proton dependence of magnetic properties. The proton switching magnetoelectricity occurs in three-dimensional molecular heterogeneous solids. It consists of a molecular magnet network as proton reservoir to modulate ferroelectric polarization, while molecular ferroelectrics charging proton transfer to reversibly manipulate magnetism. The magnetoelectric coupling induces a reversible 29% magnetization control at ferroelectric phase transition with a broad thermal hysteresis width of 160 K (192 K to 352 K), while a room-temperature reversible magnetic modulation is realized at a low electric field stimulus of 1 kV cm −1 . The findings of electrostatic proton transfer provide a pathway of proton mediated magnetization control in hierarchical molecular multiferroics.
    Free, publicly-accessible full text available December 1, 2022
  9. Abstract Epitaxial vertically aligned nanocomposites (VANs) and their related architectures have shown many intriguing features that are not available from conventional two-dimensional planar multilayers and heterostructures. The ability to control constituent, interface, microstructure, strain, and defects based on VANs has enabled the multiple degrees of freedom to manipulate the optical, magnetic, electrochemical, electronic, ionic, and superconducting properties for specific applications. This field has rapidly expanded from the interest in oxide:oxide to oxide:metal, metal:nitride and nitride:nitride systems. To achieve unparalleled properties of the materials, three-dimensional super-nanocomposites based on a hybrid of VAN and multilayer architectures have been recently explored as well. The challenges and opportunities of VAN films are also discussed in this article.
  10. In this paper, we demonstrated large-size free-standing single-crystal β-Ga 2 O 3 NMs fabricated by the hydrogen implantation and lift-off process directly from MOCVD grown β-Ga 2 O 3 epifilms on native substrates. The optimum implantation conditions were simulated with a Monte-Carlo simulation method to obtain a high hydrogen concentration with a narrow ion distribution at the desired depth. Two as grown β-Ga 2 O 3 samples with different orientations ([100] and [001]) were used to successfully create 1.2 μm thick β-Ga 2 O 3 NMs without any physical damage. These β-Ga 2 O 3 NMs were then transfer-printed onto rigid and flexible substrates such as SiC and polyimide substrates. Various material characterization studies were performed to investigate their crystal quality, surface morphologies, optical properties, mechanical properties, and bandgaps before and after the lift-off and revealed that the good material quality was maintained. This result offers several benefits in that the thickness, doping, and size of β-Ga 2 O 3 NMs can be fully controlled. Moreover, more advanced β-Ga 2 O 3 -based NM structures such as (Al x Ga 1−x ) 2 O 3 /Ga 2 O 3 heterostructure NMs can be directly created from their bulk epitaxy substrates;more »thus this study provides a viable route for the realization of high performance β-Ga 2 O 3 NM-based electronics and optoelectronics that can be built on various substrates and platforms.« less