Tuning magnetic anisotropy in Co–BaZrO 3 vertically aligned nanocomposites for memory device integration

Advanced Optical Materials

Misra

et al. 2020

Self Cite

Hyper bolic metamaterials (HMMs) have recently gained extensive research attention because of their highly anisotropic structures that lead to metallic behavior in one or two directions and dielectric features in the other(s). HMMs have great potential in applications ranging from fluorescence engineering, [7,8] nanoimaging, [2,9] sub surface sensing, [10] spontaneous [11] and thermal emissions [12,13] to single photon resources. [14] Two typical artificial struc tures including metallic nanowires (NWs) embedded in dielectric matrix (Type I: ε xx , ε yy > 0, ε zz < 0) and dielectric/metallic multi layers (MLs) (Type II: ε xx , ε yy < 0, ε zz > 0) have been shown to present hyperbolic dis persion. [15,16] Based on the hyperbolic dis persion wavelength ranges of interest, plasmonic metals such as Ag, Au, and Cu are among the best candidates in the UVvis region, and transparent conducting oxides (i.e., ITO, AZO) and transitionmetal nitrides (i.e., TiN, ZrN) are alternative plas monic materials in the nearIR wavelength region, while highly doped semiconductors are found to be alternative hyperbolic metamaterials in the midIR and longwavelength regions. [17-19] Different from the typical "topdown" techniques such as electron beam lithography (EBL), [20,21] focused ion beam (FIB), [22,23] and "bottomup" electrochemical templating methods, [24,25] the direct growth of selfassembled oxidemetal hybrid metamaterials in the vertically aligned nanocomposite (VAN) thin film form has been demonstrated as an alternative "bottomup" approach. [26-30] Interestingly, highly tunable optical properties such as localized surface plasmon resonance (LSPR) and hyperbolic dispersion shift in the UV-Vis-NIR wavelength region achieved by varying nanostructure aspect ratios, [31,32] pillar density, [32-34] and substrate selections [35,36] all present enormous potentials for these new class of hybrid thin films. Furthermore, by properly selecting the metal nanopillar phase and oxide or nitride matrix, other novel functionalities such as tunable ferroelectric, ferromagnetic, and magnetoelectric cou pling and thermal stability can also be enabled. [37-41] Very recently, a new 3D framework strain engineering has been demonstrated in oxideoxidebased thin films by stacking Dielectric-metallic hybrid metamaterials exhibit extraordinary optical properties due to the light-matter interactions at the dielectric-metallic interfaces. The ability in precision control of the light-matter interactions in nanoscale is key to tailor the optical properties of hybrid metamaterials. In this work, a complex 3D framework of multilayered self-assembled BaTiO 3 (BTO)-Au hybrid thin films is demonstrated with such precision control of the lightmatter interaction in nanoscale. Unique "bamboo-like" Au nanostructures are formed via the bilayer and trilayer stacking of BTO-Au hybrid layers with interlayers of SrTiO 3 , CeO 2 , or MgO. Different film strain states introduced by the three interlayers result in variable diameter and density of Au nanopillars. Both simulate...

Section: Introductionmentioning

confidence: 99%

Design of 3D Oxide–Metal Hybrid Metamaterial for Tailorable Light–Matter Interactions in Visible and Near‐Infrared Region

Advanced Optical Materials

Misra

et al. 2020

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“…Metal-dielectric nanocomposites as hybrid metamaterials have demonstrated a variety of physical properties and multifunctionalities toward practical applications in magnetic storage devices, photocatalysts, waveguides, smart windows, batteries, and optical metamaterials. − The anisotropic nature of these nanocomposites is usually achieved by fabricating them in either multilayer or nanowire morphology using a two-phase nanocomposite approach. ,− The hybrid materials with either metallic phase embedded inside the oxide matrix as vertical pillars or alternatively stacked in a multilayer design show very strong anisotropic physical properties, ideal for applications such as subdiffraction imaging, negative refraction, and optical magnetism. − For example, a Au/Al 2 O 3 multilayer structure with a periodic hole array through the film stack has shown a negative index at near-IR frequencies, while a Au/BaTiO 3 system with periodic Au nanowires embedded in BaTiO 3 matrix shows hyperbolic dispersion in the near-IR wavelength region. , …”

Section: Introductionmentioning

confidence: 99%

Morphology Control of Self-Assembled Three-Phase Au-BaTiO₃–ZnO Hybrid Metamaterial for Tunable Optical Properties

Misra

Crystal Growth & Design

et al. 2020

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Microstructural control in metal-dielectric hybrid metamaterials presents enormous opportunities in tailoring the physical properties including the magnetic and optical properties. Here, we demonstrate a strong tunability achieved in the microstructure of self-assembled ordered three-phase Au-BaTiO 3 −ZnO hybrid metamaterial along with its optical properties, grown by a pulsed laser deposition method. Varying the growth temperature, deposition frequency, and template thickness evolves the microstructure by tuning the Au and ZnO pillar geometry as well as the shape and size of the Au nanoparticles capping the ZnO nanowires. The three-phase hybrid metamaterials exhibit unique optical properties, including enhanced nonlinear optical properties, hyperbolic dispersion in the visible and near-infrared wavelength region, and tuned epsilon-near-zero (ENZ) wavelength upon varying the deposition parameters. This study suggests that the three-phase hybrid metamaterials present great potential in the microstructure and optical property tuning that can also be applied to other two-phase and three-phase nanocomposite systems.

“…The geometry tuning effect is not limited to optical properties. In another study of Co–BaZrO 3 (BZO) [ 64 ] nanocomposite films toward memory device integration, highly tunable magnetic anisotropy and coercive field strength have been achieved by tuning the film thickness and Co aspect ratio, which can be further easily integrated into spintronic devices. One could expect anisotropic dielectric properties in these Co–BZO films, however, not measured in this report.…”

Section: Part Ii: Permittivity Tuning In Au‐based Van Thin Filmsmentioning

confidence: 99%

Self‐Assembled Metal–Dielectric Hybrid Metamaterials in Vertically Aligned Nanocomposite Form with Tailorable Optical Properties and Coupled Multifunctionalities

Advanced Photonics Research

Wang

2021

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Metal–dielectric hybrid metamaterials have attracted increasing research interest in recent years because of their novel optical properties and promising applications in the fields of electronic and photonic devices. Dielectric permittivity is a key parameter that strongly influences the optical properties of materials. By self‐assembling the metallic and dielectric components in a pillar‐in‐matrix structure, a strong anisotropic structure forms and results in opposite signs of permittivity components (i.e., ε|| > 0 and ε⊥ < 0, or vice versa) and exotic optical responses including hyperbolic dispersion in the visible to near‐infrared region. Herein, the main approaches of tuning the permittivity in self‐assembled metal–dielectric vertically aligned nanocomposite (VAN) thin films are reviewed, including tuning the metal pillar density and geometry, film strain state and background pressure during growth, and seeking other metal‐free and complex structure designs. Future research directions are also proposed, including unique approaches to improve their thermal stability, integrate on flexible substrates toward wearable device fabrication, and explore real‐time tunable metamaterials.