Meta-optics, which is the optics for nanosized objects including the metallic and dielectric nanoparticles, have been established rapidly in recent years. One topic in meta-optics is metasurface comprising the assembly of nano particles on the surface to harness the light. We found that the metallurgy process is applicable to enhance the optical performance of metasurfaces. In this review, we describe how the rapid thermal annealing, or “nano-metallurgy process”, improves the metasurfaces via decreasing the optical loss of the nanoparticles, and introduce our experimental works demonstrating that the nano-metallurgy process indeed enhances the optical performance of the metasurfaces. We also show the examples where the thermal oxidation can make the high-quality dielectric metasurfaces. We believe that the research community of meta-optics can learn and benefit from metallurgy to establish new and interesting metasurfaces.

In general, glasses have a random structure, but they can take on unique structures due to bond selectivity. In this paper, we introduce the bond selectivity of oxygen- and fluorine-containing glasses and the formation of glass structures derived from the bond selectivity of each anion. We present the relationship between BaMgBO₃F crystals and BaF₂-MgO-B₂O₃ glasses. The crystal is composed of oxide and fluoride layers. The corresponding glass is suggested to have a bicontinuous structure from structural analysis and simulation. The glass has a favorable structure for luminescence and shows higher luminescence efficiency than the corresponding crystal. Such a structure is also favorable for nucleation; the BaF₂-ZnO-B₂O₃ glass precipitated fluoride crystals with a very small particle size distribution at 5 nm upon heat treatment. Various structural analyses suggest that the fluoride sites in the fluoride-rich domain of this glass structure are similar to the crystals. This paper suggests that various functionalities can be developed by utilizing the mixing heterogeneity derived from the selective binding of fluoride and oxide.

In this paper, we present a procedure for fabricating transparent silica glass that uses a mesoporous SiO₂-PVA(poly(vinyl alcohol)) nanocomposite as a silica glass precursor. By sintering the nanocomposite in air at 1100°C, monolithic trasnsparent silica glass was obtained with no crack. Micropatterns on the nanocomposite were fabricated by room-temperature imprinting. Micropatterned silica glass was obtained by sintering the nanocomposite at 1100°C in air. The sintered glass possessed various color photoluminescence (PL) under UV irradiation, depending on the kind of rare earth and transition metal ions.

Si₃N₄–WC composite ceramics were sintered with Al₂O₃–Y₂O₃ or AlN–Y₂O₃ at 1500°C and 1600°C in a resistance-heated hot-pressing machine. These composite ceramics were densified, except for the Si₃N₄–60 mol% WC case containing Al₂O₃–Y₂O₃. The added WC did not decompose during sintering, and no WC-derived reaction products were formed. The α-Si₃N₄ did not transform to β-SiAlON in the ceramics sintered with Al₂O₃–Y₂O₃ at 1500°C or AlN–Y₂O₃ at 1600°C, which resulted in a higher α–phase ratio in the sintered bodies. The addition of WC to Si₃N₄ ceramics sintered with Al₂O₃–Y₂O₃ at 1600°C inhibited the phase transformation from α-Si₃N₄ to β-SiAlON. The Young’s modulus for the ceramics increased with increasing WC up to 512 GPa. The Vickers hardness of the ceramics sintered with Al₂O₃–Y₂O₃ increased by increasing WC from 14.4 to 19.3 GPa. When AlN–Y₂O₃ was used as the sintering aid, the hardness increased with increasing WC, reaching a maximum of 21 GPa at 70 mol%. The Si₃N₄–70-80 mol% WC composite ceramics sintered with AlN–Y₂O₃ exhibited a high fracture toughness of 8.9 MPa m^0.5. The addition of WC to Si₃N₄ ceramics improved both hardness and fracture toughness.

Periodic arrays of silicon nanoparticles work as metasurfaces to control light at the interface. Although the combination of a variety of functional materials with metasurfaces should open a rich scientific research field, the application degree of freedom is limited severely by the fabrication process. We have developed a transfer process of silicon metasurface that uses a metallic chromium thin film as a sacrificial layer. The array of silicon nanoparticles is fabricated on the chromium thin film via electron-beam lithography and reactive ion etching. Then the metasurface is coated with a polydimethylsiloxane (PDMS) film and the successive dissolution of the chromium layer by an acidic solution results in the self-standing sticker embedding the metasurface. The metasurface sticker shows the optical diffraction behavior predicted from the periodicity of the array, and the transfer is performed without disturbing the periodicity. The sticker is flexible and can be attached to any clean surfaces without special surface treatment. We combine the silicon metasurface sticker with an emitter layer to control the light emission through the sticker. This result extends the application area of the metasurface.