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

Abstract

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...

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

“…[68][69][70][71][72] A recent demonstration in the case of metal-dielectric VAN system focuses on a set of 3D multilayered (ML) Au-BTO hybrid films separated by various dielectric interlayers (STO, CeO 2 , MgO) deposited on STO (001) by PLD. [73] Different interlayer materials lead to various IP lattice strains for the Au-BTO hybrid films. The cross-sectional STEM images with corresponding EDS mappings of Au-BTO bilayer films with STO, CeO 2 , and MgO interlayers are shown in Figure 5a1-a2, b1-b2, and c1-c2, respectively.…”

“…In addition to the hyperbolic dispersion resulted from the strong anisotropy due to the vertical nanopillar structure, the strong strain coupling effect in the VAN structures causes the lattice distortion and noncentrosymmetry which lead to other interesting optical properties, such as the optical nonlinearity and bandgap tuning within the hybrid thin films. [43,73,111] The following examples show that, by incorporating versatile material components into the VAN framework, the metal-dielectric hybrid nanocomposites exhibit various physical properties which could have a wide range of potential applications in different fields.…”

“…Inset shows its isofrequency surfaces in k-space at 900 nm. Reproduced with permission [73]. Copyright 2020, Wiley-VCH.…”

Recent Advances in Vertically Aligned Nanocomposites with Tunable Optical Anisotropy: Fundamentals and Beyond

“…In terms of functionality, BTO exhibits ferroelectric property while Au exhibits strong plasmonic resonance at nanoscale [75]. As a result, the VAN structure exhibits distinct Au nanopillars and BTO matrix without intermixing or discontinuity [56,76]. The Au nanopillars possess a diameter of around 20 nm and a relatively uniform distribution as visualized from plan-view and cross-section energy-dispersive X-ray spectroscopy (EDX) mapping (Figure 4b).…”

“…There are few studies investigating the thermal stability of some oxide-metal VANs, which have provided some promising feedback. For example, a complex interlayered BTO-Au/STO/BTO-Au heterostructure is displayed in Figure 8j [76]. In-situ thermal stability test is conducted inside a TEM column where no obvious morphological change is observed upon 600 • C annealing.…”