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1. Hybrid Ag–LiNbO 3 nanocomposite thin films with tailorable optical properties

   https://doi.org/10.1039/D0NA00975J  

   Huang, Jijie ; Zhang, Di ; Qi, Zhimin ; Zhang, Bruce ; Wang, Haiyan ( February 2021 , Nanoscale Advances)

   null (Ed.)

   Ag nanostructures exhibit extraordinary optical properties, which are important for photonic device integration. Herein, we deposited Ag–LiNbO 3 (LNO) nanocomposite thin films with Ag nanoparticles (NPs) embedded into the LNO matrix by the co-deposition of Ag and LNO using a pulsed laser deposition (PLD) method. The density and size of Ag NPs were tailored by varying the Ag composition. Low-density and high-density Ag–LNO nanocomposite thin films were deposited and their optical properties, such as transmittance spectra, ellipsometry measurement, as well as angle-dependent and polarization-resolved reflectivity spectra, were explored. The Ag–LNO films show surface plasmon resonance (SPR) in the visible range, tunable optical constants and optical anisotropy, which are critical for photonic device applications. 

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2. TiN‐Au/HfO 2 ‐Au Multilayer Thin Films with Tunable Hyperbolic Optical Response

   https://doi.org/10.1002/smtd.202400087  

   Zhang, Yizhi ; Shen, Jianan ; Tsai, Benson Kunhung ; Sheng, Xuanyu ; Hu, Zedong ; Zhang, Xinghang ; Wang, Haiyan ( March 2024 , Small Methods)

   Hyperbolic metamaterials (HMM) possess significant anisotropic physical properties and tunability and thus find many applications in integrated photonic devices. HMMs consisting of metal and dielectric phases in either multilayer or vertically aligned nanocomposites (VAN) form are demonstrated with different hyperbolic properties. Herein, self‐assembled HfO₂‐Au/TiN‐Au multilayer thin films, combining both the multilayer and VAN designs, are demonstrated. Specifically, Au nanopillars embedded in HfO₂and TiN layers forming the alternative layers of HfO₂‐Au VAN and TiN‐Au VAN. The HfO₂and TiN layer thickness is carefully controlled by varying laser pulses during pulsed laser deposition (PLD). Interestingly, tunable anisotropic physical properties can be achieved by adjusting the bi‐layer thickness and the number of the bi‐layers. Type II optical hyperbolic dispersion can be obtained from high layer thickness structure (e.g., 20 nm), while it can be transformed into Type I optical hyperbolic dispersion by reducing the thickness to a proper value (e.g., 4 nm). This new nanoscale hybrid metamaterial structure with the three‐phase VAN design shows great potential for tailorable optical components in future integrated devices.

    

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3. Natural van der Waals heterostructure cylindrite with highly anisotropic optical responses

   https://doi.org/10.1038/s41699-021-00254-9  

   Dasgupta, Arindam ; Gao, Jie ; Yang, Xiaodong ( August 2021 , npj 2D Materials and Applications)

   The mechanical exfoliation of naturally occurring layered materials has emerged as an easy and effective method for achieving ultrathin van der Waals (vdW) heterostructures with well-defined lattice orientations of the constituent two-dimensional (2D) material layers. Cylindrite is one such naturally occurring vdW heterostructure, where the superlattice is composed of alternating stacks of SnS₂-like and PbS-like layers. Although the constituent 2D lattices are isotropic, inhomogeneous strain occurring from local atomic alignment for forcing the commensuration makes the cylindrite superlattice structurally anisotropic. Here, we demonstrate the highly anisotropic optical responses of cylindrite thin flakes induced by the anisotropic crystal structure, including angle-resolved polarized Raman scattering, linear dichroism, and polarization-dependent anisotropic third-harmonic generation. Our results provide a promising approach for identifying various natural vdW heterostructure-based 2D materials with tailored optical properties and can be harnessed for realizing anisotropic optical devices for on-chip photonic circuits and optical information processing.

    

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4. Self-assembled HfO 2 -Au nanocomposites with ultra-fine vertically aligned Au nanopillars

   https://doi.org/10.1039/D2NR03104C  

   Zhang, Yizhi ; Zhang, Di ; Liu, Juncheng ; Lu, Ping ; Deitz, Julia ; Shen, Jianan ; He, Zihao ; Zhang, Xinghang ; Wang, Haiyan ( August 2022 , Nanoscale)

   Oxide-metal-based hybrid materials have gained great research interest in recent years owing to their potential for multifunctionality, property coupling, and tunability. Specifically, oxide-metal hybrid materials in a vertically aligned nanocomposite (VAN) form could produce pronounced anisotropic physical properties, e.g. , hyperbolic optical properties. Herein, self-assembled HfO 2 -Au nanocomposites with ultra-fine vertically aligned Au nanopillars (as fine as 3 nm in diameter) embedded in a HfO 2 matrix were fabricated using a one-step self-assembly process. The film crystallinity and pillar uniformity can be obviously improved by adding an ultra-thin TiN-Au buffer layer during the growth. The HfO 2 -Au hybrid VAN films show an obvious plasmonic resonance at 480 nm, which is much lower than the typical plasmonic resonance wavelength of Au nanostructures, and is attributed to the well-aligned ultra-fine Au nanopillars. Coupled with the broad hyperbolic dispersion ranging from 1050 nm to 1800 nm in wavelength, and unique dielectric HfO 2 , this nanoscale hybrid plasmonic metamaterial presents strong potential for the design of future integrated optical and electronic switching devices. 

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5. Tunable Magnetic and Optical Anisotropy in ZrO 2 ‐Co Vertically Aligned Nanocomposites

   https://doi.org/10.1002/admi.202300150  

   Zhang, Yizhi ; Song, Jiawei ; Lu, Ping ; Deitz, Julia ; Zhang, Di ; Dou, Hongyi ; Shen, Jianan ; Hu, Zedong ; Zhang, Xinghang ; Wang, Haiyan ( May 2023 , Advanced Materials Interfaces)

   Metamaterials have gained great research interest in recent years owing to their potential for property tunability, multifunctionality, and property coupling. As a new group of self‐assembled thin films, vertically aligned nanocomposite (VAN)‐based hybrid metamaterials have been demonstrated with significant anisotropic physical properties and a broad range of property tailorability, such as optical anisotropy, magnetic anisotropy, hyperbolic dispersion, and enhanced second harmonic generation properties. Herein, self‐assembled ZrO₂‐Co nanocomposite films, with high epitaxial quality and ultra‐fine vertically aligned Co nanopillars (with an average diameter of ≈2 nm) embedded in a ZrO₂matrix, are fabricated using a pulsed laser deposition (PLD) method. The Co pillar density can be effectively tuned by varying the Co concentration in the target, which results in tunable optical properties and magnetic properties. Specifically, a high saturation magnetization of 100 emu cm⁻³, strong out‐of‐plane magnetic anisotropy and tailorable magnetization properties are achieved via tuning the Co nanopillar density. Coupled with hyperbolic dispersion of dielectric constant from 950 to 1500 nm in wavelength, plasmonic Co metal nanopillars, and the unique dielectric ZrO₂matrix, this new nanoscale hybrid metamaterial shows great potential for future integrated optical and magnetic device designs.

    

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