Metal-Free Oxide-Nitride Heterostructure as a Tunable Hyperbolic Metamaterial Platform

Abstract

Metal-free plasmonic metamaterials with wide-range tunable optical properties are highly desired for various components in future integrated optical devices. Designing a ceramic–ceramic hybrid metamaterial has been theoretically proposed as a solution to this critical optical material demand. However, the processing of such all-ceramic metamaterials is challenging due to difficulties in integrating two very dissimilar ceramic phases as one hybrid system. In this work, an oxide-nitride hybrid metamaterial combining two highly dissimilar ceramic phases, i.e., semiconducting weak ferromagnetic NiO nanorods and conductive plasmonic TiN matrix, has been successfully integrated as a unique vertically aligned nanocomposite form. Highly anisotropic optical properties such as hyperbolic dispersions and strong magneto-optical coupling have been demonstrated under room temperature. The novel functionalities presented show the strong potentials of this new ceramic–ceramic hybrid thin film platform and its future applications in next-generation nanophotonics and magneto-optical integrated devices without the lossy metallic components.

Nitride‐Oxide‐Metal Heterostructure with Self‐Assembled Core–Shell Nanopillar Arrays: Effect of Ordering on Magneto‐Optical Properties

“…[ 43,44 ] Here, nanoscale NiO exhibits weak FM property as reported by prior studies. [ 45–47 ] Au exhibits good plasmonic properties and catalytic properties facilitating the nanowire growth. [ 48 ] Two growth processes were taken to explore the potentials in achieving ordered three‐phase structure as illustrated in Figure 1B: 1) a direct co‐deposition of three phases, 2) a template growth to direct the NiO nucleation on top of Au nanopillars.…”

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

“…The permittivity of one typical metal–nitride Au–TiN [ 58 ] hybrid film is also shown in the plot, where the majority of ε || and ε ⊥ are all negative because of the metallic behaviors of both Au and TiN. More interestingly, a very recent study has demonstrated the NiO–TiN [ 59 ] hybrid VAN thin film, where the dielectric NiO phase presents the nanopillar morphology grown in the metallic TiN matrix, leading to ε || < 0, ε ⊥ > 0 with permittivity mainly located in the second quadrant (schematic illustration shown on the top left in the diagram). Table 1 summarizes the IP ( ε || ) and OP ( ε ⊥ ) permittivity values and functionalities for the reported VAN systems in the wavelength range of 400–1000 nm.…”

“…[47][48][49][50][51][52] The permittivity of common oxides, nitrides, carbides, and several explored VAN hybrid system in the wavelength range of 400-1000 nm are plotted in Figure 2. [45][46][47][48][49][50][51][52][53][54][55][56][57][58][59] It can be seen that most of the pure oxides, carbides, and nitrides have isotropic positive permittivity values, i.e., nearly equal positive ε || and ε ⊥ values due to the (pseudo-) centrosymmetric structures. Thus the range of their permittivity values are located in the light-blue elliptical region in the first quadrant of the diagram, with a few exceptions of transition metal nitrides (i.e., TiN, HfN, and ZrN) with both negative ε || and ε ⊥ located in the third quadrant of the diagram.…”

“…IP (ε || ) and OP (ε ⊥ ) permittivity diagram of oxides, nitrides, carbides, and several reported metal-oxide, oxide-oxide VAN systems at wavelength from 400 to 1000 nm. [45][46][47][48][49][50][51][52][53][54][55][56][57][58][59] Insets are two schematic illustrations of two types of VAN hybrid films: i) ε || > 0, ε ⊥ < 0 (shown on bottom right) and ii) ε || < 0, ε ⊥ > 0 (shown on top left).…”

“…[108,109] Hence, in a very recent work, the conductive plasmonic TiN has been combined with the dielectric and weak ferromagnetic nickel oxide (NiO) phase to form a new nitride-oxide VAN structured film. [59] The cross-sectional and plan-view STEM images of the TiN-NiO hybrid film are shown in Figure 8g,h. It is clear that TiN and NiO grow separately, where the NiO performs nanorods morphology and are uniformly distributed in the TiN matrix with clear interfaces.…”