Room-Temperature Ferroelectric LiNb₆Ba₅Ti₄O₃₀ Spinel Phase in a Nanocomposite Thin Film Form for Nonlinear Photonics

Abstract

Tetragonal tungsten bronze (TTB) materials are one of the most promising classes of materials for ferroelectric and nonlinear optical devices, owing to their very unique noncentrosymmetric crystal structure. In this work, a new TTB phase of LiNb6Ba5Ti4O30 (LNBTO) has been discovered and studied. A small amount of a secondary phase, LiTiO2 (LTO), has been incorporated as nanopillars that are vertically embedded in the LNBTO matrix. The new multifunctional nanocomposite thin film presents exotic highly anisotropic microstructure and properties, e.g., strong ferroelectricity, high optical transparency, anisotropic dielectric function, and strong optical nonlinearity evidenced by the second harmonic generation results. An optical waveguide structure based on the stacks of α-Si on SiO2/LNBTO–LTO has been fabricated, exhibiting low optical dispersion with an optimized evanescent field staying in the LNBTO–LTO active layer. This work highlights the combination of new TTB material designs and vertically aligned nanocomposite structures for further enhanced anisotropic and nonlinear properties.

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

“…[ 113 ] Therefore, due to the anisotropic nanostructure and lattice strain coupling at the pillar/matrix and film/substrate interfaces, the VAN hybrid thin films are expected to have enhanced SHG response compared with the pure NLO materials. [ 43,102,111 ] More interestingly, noncentrosymmetric and anisotropic nature has been demonstrated in the Au–TaN hybrid thin film with both phases of centrosymmetric crystal structures. [ 45 ] The comparison of the SHG intensity of TaN and Au–TaN films as a function of incident polarization angle fixed at 0° (P‐out) and 90° (S‐out) are shown in Figure a,b, 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.…”

“…Different from those techniques, a direct growth of self‐assembled vertically aligned nanocomposite (VAN) thin films could be an alternative approach and has been demonstrated in various oxide–oxide, metal–oxide, and metal–nitride material systems via a pulsed laser deposition (PLD) technique. [ 38–45 ] The scanning transmission electron microscopy (STEM) image and electron dispersive X‐ray spectroscopy (EDS) of Au–BaTiO 3 (BTO) hybrid metamaterial is chosen as an example and shown in Figure 1c–d, where vertical straight Au nanopillars are embedded in the BTO matrix to form a typical VAN structure. Due to the strong anisotropic structure of the vertical Au nanopillars, the real permittivity of the film (Figure 1e) IP () and OP () components show quite different trends, i.e., remains positive in the entire wavelength region while decreases from positive to negative at 824 nm.…”

Ultrathin Ternary FeCoNi Alloy Nanoarrays in BaTiO3 Matrix for Room-Temperature Multiferroic and Hyperbolic Metamaterial

“…Moreover, a deeper understanding of the growth mechanisms underlying different nanocomposite thin film systems is essential, as various nanostructures were obtained such as the typical nanopillarin-matrix, 12 core−shell nanopillar-in-matrix, 13 and nanoparticle-in-matrix, 43 in addition to the emergence of new phases. 44 Lastly, leveraging the multifunctionality inherent in oxide-alloy VANs, particularly exemplified by the BTO-FCN system, holds immense potential for integrating multiple functionalities into a single device platform. By exploitation of the synergistic interactions between the oxide and alloy components, novel device architectures with enhanced performance characteristics can be envisioned, paving the way for transformative advancements in various technological domains.…”