Second-harmonic generation (SHG) in nanostructures gives rise to many applications such as lab-on-a-chip and imaging by frequency doubling. However, the SHG signal decreases with volume, and the conversion efficiency is limited. Thus, means to enhance nonlinear signals at the nanoscale are needed. For instance, while plasmonic nanostructures offer a high enhancement due to the strong confinement of the electromagnetic field, they have high losses and the fabrication methods are difficult. In this work, we propose to enhance the SHG by using the intrinsic scattering properties of an all-dielectric perovskite nanostructure. We demonstrate the Mie scattering resonances of individual barium titanate (BaTiO 3 ) nanoparticles with diameters between 200 and 250 nm. We distinguish contributions of the magnetic dipole and magnetic quadrupole. Then, we use the Mie resonances to achieve an SHG enhancement of 4 orders of magnitude within the same nanoparticle. Our results suggest that a strong increase of the SHG signal can be obtained without using plasmonic or hybrid nanostructures. We show a straightforward way of enhancing low optical signals within a single material, which will facilitate the study of other nonlinear phenomena at the nanoscale.

We show enhanced second-harmonic generation (SHG) from a hybrid metal-dielectric nanodimer consisting of an inorganic perovskite nanoparticle of barium titanate (BaTiO) coupled to a metallic gold (Au) nanoparticle. BaTiO-Au nanodimers of 100 nm/80 nm sizes are fabricated by sequential capillarity-assisted particle assembly. The BaTiO nanoparticle has a noncentrosymmetric crystalline structure and generates bulk SHG. We use the localized surface plasmon resonance of the gold nanoparticle to enhance the SHG from the BaTiO nanoparticle. We experimentally measure the nonlinear signal from assembled nanodimers and demonstrate an up to 15-fold enhancement compared to a single BaTiO nanoparticle. We further perform numerical simulations of the linear and SHG spectra of the BaTiO-Au nanodimer and show that the gold nanoparticle acts as a nanoantenna at the SHG wavelength.

We demonstrate a readily scalable print, lift, and stack approach for producing large-area, 3D photonic crystal (PC) structures and optical gratings. UV-assisted nanoimprint lithography was used to pattern grating structures composed of highly filled nanoparticle (NP) polymer composite resists with tunable refractive indices (RI). The gratings were robust and upon release from a support substrate were oriented and stacked to yield 3D PCs. The composite resists were composed of anatase titania (TiO 2 ) NPs, between 5 and 30 nm in diameter, and a UV-curable optical resist (Norland Optical Adhesive 60). The RI of the composite resists was tuned between 1.58 and 1.92 at 800 nm while maintaining excellent optical transparency. The grating structure dimensions, line width, depth, and pitch were easily varied by simply changing the imprint mold. A six-layer log-pile stack was prepared using a composite resist containing 50 wt % TiO 2 NPs with an RI of 1.72 and yielded up to 72% reflection at 840 nm and a minimum reflection of 50% over broad angles of incidence (25−65°) and grating areas of >6 cm 2 . The grating patterning process is readily scalable for roll-to-roll production, and the ability to tailor RI as well as grating structure dimensions and orientation offers an attractive means for large-area production of tuned optical materials, while automating alignment will enable high-volume production of PCs.

We introduce a novel method to easily fabricate nanopatterns at ambient conditions using solvent-assisted soft nanolithography. For this purpose, a P3HT/PCBM bilayer, one of well-known standard models of solar cell systems, was chosen to optimize bilayer solar cells using the new lithographic technique. The nanopatterns of P3HT made using this method have improved device efficiency compared to planar bilayer heterojunction of the solar cell. The new patterning process creates solar cell devices with a greater than 2-fold increase in power conversion efficiency (PCE) compared to an otherwise equivalent, flat device. This improvement in efficiency is due to the increased interfacial area created by the patterning process. This result demonstrates the feasibility of extensive applications toward nanolithography, relevant to device fabrication, such as electronic devices.

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