Asymmetric nanocavities with wide reflection color gamut for color printing.

Symmetric metal-dielectric-metal (MDM) nanocavities based on Fabry-Perot resonance play a crucial role in transmission colors. However, their reflection color gamuts are generally limited owing to the narrow dip of resonance spectrum. In this work, we propose and fabricate symmetric titanium-indium tin oxide-silver (Ti/ITO/Ag) nanocavities to realize the reflection colors. The experimental and simulation results show that reflection color gamut of the asymmetric nanocavity is wider than that of symmetric MDM nanocavity due to the generation of broader resonance spectral dip. Moreover, a grayscale focused ion beam (FIB) etching method is employed to fabricate the thickness-controlled microstructures, and the etching depth satisfies a linear relationship with the gray value. The reflection color image can be observed by fabricating the ITO layer in the asymmetric MDM nanocavity with grayscale FIB etching method, which is more vivid than the image from fabricated symmetric MDM nanocavities. This work will provide a new way for color printing, color display, and ultra-small anti-counterfeiting technology.