Structural Colors Based on Diamond Metasurface for Information Encryption

Abstract

Structural colors based on dielectric metasurfaces are attractive because of their potential application in next‐generation color printing. However, the commonly used dielectric materials suffer from issues of high light absorption (e.g., Si at blue wavelength) and low resistance to corrosion (e.g., titanium oxide), which greatly limit their application as structural color for information encryption. Here, dielectric‐metasurface‐based structural color constructed on nanocrystalline diamond (NCD) film by using bias enhanced nucleation (BEN) technique is demonstrated. Owing to the formation of highly crystalline diamond by the BEN process, the synthesized NCD film with a thickness of ~500 nm exhibits excellent optical quality with a relatively high refractive index that produces a strong magnetic dipole mode by Mie resonance. To realize the dynamic functionalities of diamond‐metasurface color with high resolution, a periodic array of asymmetric diamond cuboids with high aspect ratio (≈3.1) is fabricated, which produces polarization‐dependent response due to the enhanced Mie resonance. By optimizing the configuration of the diamond‐metasurface system, the color performance is improved with high brightness and a relatively wide gamut. This work demonstrates for the first time that NCD can serve as a robust and highly tunable dielectric platform for application in information encryption.

Recent progress on structural coloration

“…This approach allows color switching without changing the geometric shape or material composition. Numerous studies have explored polarizationdependent structural colors for applications such as dynamic color displays, high-density optical information storage, optical encryption, and multi-channel imaging [51,178,219,220] . Due to the optical anisotropy of liquid crystals (LCs), they exhibit different refractive indices in different directions, resulting in phase delays along different directions.…”

“…While Si has a high refractive index, its unavoidable absorption losses at short wavelengths result in low efficiency and reduced saturation due to the broadening of the bandwidth in visible range. To address the optical characteristics of the material itself, researchers have turned to dielectric materials with negligible losses in the visible light range, such as titanium dioxide (TiO2) [141–143] , silicon nitride (Si3normalN4) [144–146] , and so on [51,147,148] . Among these, TiO2, with its excellent optical properties and compatibility with CMOS processes, has found extensive use in the field of optics [149–151] .…”

“…This approach allows color switching without changing the geometric shape or material composition. Numerous studies have explored polarization-dependent structural colors for applications such as dynamic color displays, high-density optical information storage, optical encryption, and multi-channel imaging [51,178,219,220] .…”

“…Given the stringent requirements of micro displays for integration and resolution, structural colors have been widely explored as the foundation for the next generation of micro display devices. Apart from their application in conventional color displays, structural colors find extensive use in optical information storage due to their high spatial resolution and superb polarization tunability [49–53] . Owing to the unique response of nanostructures to the light field, structural colors are employed in optical encryption and steganography, providing enhanced security features at the nanoscale [54–56] .…”