Thermally-curable nanocomposite printing for the scalable manufacturing of dielectric metasurfaces

Abstract

Metasurfaces consisting of artificially designed meta-atoms have been popularized recently due to their advantages of amplitude and phase of light control. However, the electron beam lithography method for metasurface fabrication has high cost and low throughput, which results in a limitation for the fabrication of metasurfaces. In this study, nanocomposite printing technology is used to fabricate high-efficiency metasurfaces with low cost. To demonstrate the efficiency of the proposed fabrication method, a metahologram is designed and fabricated using a nanocomposite. The metahologram exhibits conversion efficiencies of 48% and 35% at wavelengths of 532 and 635 nm, respectively. The nanocomposite is composed of polymers with nanoparticles, so durability tests are also performed to evaluate the effects of temperature and humidity on the metasurfaces. The test verifies that at temperatures below the glass transition temperature of the base resin, the nanostructures do not collapse, so the efficiency of the metasurfaces remains almost the same. The surrounding humidity does not affect the nanostructures at all. Hence, the durability of the nanocomposite metasurfaces can be further enhanced by replacing the base resin, and this nanocomposite printing method will facilitate practical metasurface use at low cost.

Keywords: Micro-optics; Nanoparticles; Nanophotonics and plasmonics; Structural properties.

Fig. 1

Schematic of metasurface fabrication by nanocomposite printing

Fig. 2. Effect of temperature on PER nanostructures.

a Original PER nanostructures. b–f PER nanostructures after 4 h of annealing at different temperatures at a surrounding humidity of 30%. The PER patterns begin to collapse above 90 °C, which corresponds to the glass transition temperature of the base resin

Fig. 3. Effect of humidity on PER nanostructures. The test sample is identical to that of the temperature test.

a–c PER nanostructures after 4 h in a humidity-controlled chamber. d PER nanostructures after soaking in water. The PER nanostructures are not affected by the surrounding humidity

Fig. 4. Optical properties of TiO₂ PER thin films.

a Refractive index (dashed lines) and extinction coefficient (solid lines) according to TiO₂ nanoparticle concentration following solvent removal. b SEM image of a spin-coated 80% TiO₂ nanoparticle layer on a glass substrate. Optical properties of TiO₂ PER thin films: (c) measured refractive index and extinction coefficient and (d) simulated transmission of 80 wt% PER. The transmission is simulated at λ = 532 nm. e Refractive index and (f) simulated transmission of 89 wt% PER. The transmission is simulated at λ = 635 nm

Fig. 5. Scanning electron microscopy (SEM) images.

a Si master stamp, b h-PDMS polymer replica. c, d TiO₂ 80% nanoparticle PER nanostructures

Fig. 6. Captured holographic images produced by TiO₂ PER metaholograms with different concentrations.

Measurement results at λ = 532 nm with concentrations of (a) 67 wt%, (b) 80 wt%, (c) 86 wt%, and (d) 89 wt% and at λ = 635 nm with concentrations of (e) 67 wt%, (f) 80 wt%, (g) 86 wt%, and (h) 89 wt%. i Measured hologram efficiency according to TiO₂ PER concentration

Fig. 7

Measured hologram efficiency according to TiO₂ PER concentration

Fig. 8. Captured holographic images generated from TiO₂ PER metaholograms.

They are fabricated on (a) and (d) flat, (b) and (e) flexible, and (c) and (f) curved substrates. Metaholograms following the durability test: (g) SEM image and (h) generated hologram after 24 h at 70 °C and 70% humidity