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1. Self-assembled nitride–metal nanocomposites: recent progress and future prospects

   https://doi.org/10.1039/d0nr06316a  

   Wang, Xuejing; Wang, Haiyan (October 2020, Nanoscale)

   null (Ed.)

   Two-phase nanocomposites have gained significant research interest because of their multifunctionalities, tunable geometries and potential device applications. Different from the previously demonstrated oxide–oxide 2-phase nanocomposites, coupling nitrides with metals shows high potential for building alternative hybrid plasmonic metamaterials towards chemical sensing, tunable plasmonics, and nonlinear optics. Unique advantages, including distinct atomic interface, excellent crystalline quality, large-scale surface coverage and durable solid-state platform, address the high demand for new hybrid metamaterial designs for versatile optical material needs. This review summarizes the recent progress on nitride–metal nanocomposites, specifically targeting bottom-up self-assembled nanocomposite thin films. Various morphologies including vertically aligned nanocomposites (VANs), self-organized nanoinclusions, and nanoholes fabricated by additional chemical treatments are introduced. Starting from thin film nucleation and growth, the prerequisites of successful strain coupling and the underlying growth mechanisms are discussed. These findings facilitate a better control of tunable nanostructures and optical functionalities. Future research directions are proposed, including morphological control of the secondary phase to enhance its homogeneity, coupling nitrides with magnetic phase for the magneto-optical effect and growing all-ceramic nanocomposites to extend functionalities and anisotropy. 

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2. Reducing leakage current and enhancing polarization in multiferroic 3D super-nanocomposites by microstructure engineering

   https://doi.org/10.1088/1361-6528/ac5f98  

   Enriquez, Erik; Lu, Ping; Li, Leigang; Zhang, Bruce; Wang, Haiyan; Jia, Quanxi; Chen, Aiping (July 2022, Nanotechnology)

   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. 

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3. Thermal stability of self-assembled ordered three-phase Au–BaTiO ₃ –ZnO nanocomposite thin films via in situ heating in TEM

   https://doi.org/10.1039/d0nr06115h  

   Misra, Shikhar; Zhang, Di; Lu, Ping; Wang, Haiyan (December 2020, Nanoscale)

   null (Ed.)

   Thermal stability of oxide–metal nanocomposites is important for designing practical devices for high temperature applications. Here, we study the thermal stability of the self-assembled ordered three-phase Au–BaTiO 3 –ZnO nanocomposite by both ex situ annealing under air and vacuum conditions, and by in situ heating in TEM in a vacuum. The study reveals that the variation of the annealing conditions greatly affects the resulting microstructure and the associated dominant diffusion mechanism. Specifically, Au nanoparticles show coarsening upon air annealing, while Au and Zn either form a solid solution, with Zn atomic percentage less than 10%, or undergo a reverse Vapor–Liquid–Solid (VLS) mechanism upon vacuum annealing. The distinct microstructures obtained also show different permittivity response in the visible and near-infrared region, while retaining their hyperbolic dispersion characteristics enabled by their highly anisotropic structures. Such in situ heating study in TEM provides critical information about microstructure evolution, growth mechanisms at the nanoscale, and thermal stability of the multi-phase nanocomposites for future electronic device applications. 

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4. Microphase Separation‐Driven Sequential Self‐Folding of Nanocomposite Hydrogel/Elastomer Actuators

   https://doi.org/10.1002/adfm.202200157  

   Zhao, Jiayu; Bae, Jinhye (March 2022, Advanced Functional Materials)

   Abstract Untethered stimuli‐responsive soft materials with programmed sequential self‐folding are of great interest due to their ability to achieve task‐specific shape transformation with complex final configuration. Here, reversible and sequential self‐folding soft actuators are demonstrated by utilizing a temperature‐responsive nanocomposite hydrogel with different folding speeds but the same chemical composition. By varying the UV light intensity during the photo‐crosslinking of the nanocomposite hydrogel, different types of microstructures can be realized via phase separation mechanisms, which allow to control the folding speeds. The self‐folding structures are fabricated by integrating two dissimilar materials (i.e., a nanocomposite hydrogel and an elastomer) into hinge‐based bilayer structures via extrusion‐based 3D printing. It has been demonstrated that the folding kinetics can be accelerated by more than one order of magnitude due to the phase‐separated microstructure formed by the relatively weaker UV intensity (≈10 mW cm^‐2) compared to the one formed by stronger UV intensity (≈100 mW cm^‐2). 3D structures with sequential self‐folding capabilities are realized by prescribing actuation speeds and folding angles to specific hinges of the nanocomposite hydrogel. Sequential folding box and self‐locking latch structures are fabricated to demonstrate the ability to capture and hold objects underwater. 

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5. A material design guideline for self-assembled vertically aligned nanocomposite thin films

   https://doi.org/10.1088/2515-7639/ad9bee  

   Song, Jiawei; Wang, Haiyan (January 2025, Journal of Physics: Materials)

   Abstract Nanocomposite thin films, comprising two or more distinct materials at nanoscale, have attracted significant research interest considering their potential of integrating multiple functionalities for advanced applications in electronics, energy storage, photonics, photovoltaics, and sensing. Among various fabrication technologies, a one-step pulsed laser deposition process enables the self-assembly of materials into vertically aligned nanocomposites (VANs). The demonstrated VAN systems include oxide–oxide, oxide–metal, and nitride–metal VAN films and their growth mechanisms are vastly different. These complexities pose challenges in the designs, materials selection, and prediction of the resulted VAN morphologies and properties. The review examines the key roles that surface energy plays in the VAN growth and provides a generalized materials design guideline combining the two key factors of surface energy and lattice strain/mismatch, along with other factors related to growth kinetics that collectively influence the morphology of VAN films. This review aims to offer valuable guidelines for future material selection and microstructure design in the development of self-assembled VAN films. 

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