Structural color based on a TiO ₂ semi-ellipsoidal nanostructures metasurface

Structural colors, an emerging pigment-free coloration technology, have attracted significant attention in recent years. TiO₂-based all-dielectric metasurfaces exhibit outstanding performance in color saturation and loss control. However, in single-dielectric systems, multipolar modes, especially higher-order ones, are easily excited at nonresonant wavelengths, leading to undesired subsidiary peaks in the reflection spectrum and a reduction in color saturation. To address this problem, we propose and demonstrate a design with all-TiO₂ semi-ellipsoidal nanostructures as the unit cell. The continuously varying surface profile effectively suppresses higher-order modes. As a result, in contrast to nanostructures with abrupt geometric discontinuities, the metasurface can achieve high reflectance with narrow FWHM reflection peaks and cover a color range from blue-green to orange-red without relying on multilayer dielectric stacks. The fabricated semi-ellipsoidal TiO₂ nanostructures with specific periodicity achieved high saturation and pure color in structural coloration, when the reflectance spectrum exhibits a narrowband feature. This strategy not only affords additional degrees of freedom in geometric design but also reduces the complexity associated with material deposition and the fabrication of nanostructures featuring curved surfaces, thereby providing an avenue for the realization of structural color display devices with enhanced color purity.