Large-Area Printing of Optical Gratings and 3D Photonic Crystals Using Solution-Processable Nanoparticle/Polymer Composites

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 (TiO2) 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 % TiO2 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 cm2. 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.