Mono-layered Photonic Crystal Patterning for Anti-counterfeit Applications of Structural Colors

Abstract

Photonic crystals (PCs) can manipulate electromagnetic wave by designing artificial periodic dielectrics, which provides various applications such as sensor, LED, laser, and optical computers. Recently, many studies focus on display applications by designing photonic band-gap while the fabrication of photonic crystals in a nanoscale is still challenging. In this work, a simple method is described for fabricating mono-layered self-assembled photonic crystals (SAPCs) by using inkjet material printers that are able to inject nanoparticle suspension on a substrate in contrast to conventional approaches such as photo-lithography, two-photon patterning, and direct-write assembly. For making homogeneous single-layered structure, crucial factors influencing the micro-patterns of a colloidal assembly of the inkjet-printed droplet were investigated including the substrate wettability and chemical composition of ink to see what effect they might have on producing structure color. These patterned photonic crystals yield stealth ability to avoid pattern detection from counterfeiters under day light illumination and generate multiple colorful holograms on different viewing angles for complex cryptography. In addition, the number of SAPCs in a matrix format controls optical intensities, thus yielding extra anti-counterfeiting function. Because the inkjet-printed-based SAPC platforms provides a simple and the unique optical properties, it is believed that the approach can be widely used for anti-counterfeiting systems.