# The iridescence of disordered resonant metasurfaces

**Authors:** A. Agreda, T. Wu, A. Hereu, M. Treguer-Delapierre, G. L. Drisko, K. Vynck, P. Lalanne  
**arXiv:** [2211.09520](https://arxiv.org/abs/2211.09520)  
**Date:** 2022-11-17  
**Summary page:** https://www.summarizepaper.com/en/paper/2211.09520v1/

## Key points

- Light interacting with micro- and nano-scale structures in nature produces beautiful colors
- Engineers are designing nanophotonic systems for achieving angle-insensitive structural colors or prescribed angular color response
- Artificial optical metasurfaces composed of monolayers of Mie or plasmonic nanoresonators have recently attracted considerable attention for various applications, including color generation
- Researchers studied the iridescence of disordered metasurfaces made by large silver nanoparticles deposited on a reflective substrate coated with a submicrometric dielectric spacer
- The researchers demonstrated a remarkable iridescence phenomenon with only two distinct colors using solar simulation
- The metasurfaces were fabricated by dip-coating a SiO2/Si wafer with a colloidal monolayer of silver nanocubes
- The study gathered experimental results for samples obtained with moderate silver nanocube densities and SiO2 layer thicknesses ranging from 0 nm to 700 nm
- Overall, this work highlights uncommon iridescences that differ from those classically observed with natural nanostructures or thin-film interferences.

## Summary

The interaction of light with micro- and nano-scale structures in nature produces beautiful colors and visual appearances, inspiring engineers to design nanophotonic systems for achieving angle-insensitive structural colors or prescribed angular color response. Artificial optical metasurfaces composed of monolayers of Mie or plasmonic nanoresonators have recently attracted considerable attention for various applications, including color generation. These metasurfaces offer many degrees of freedom that are not encountered in nature, allowing for the tailoring of resonances using a plethora of high-index materials and shapes at the nanoscale. In this work, researchers studied the iridescence of disordered metasurfaces made by large silver nanoparticles deposited on a reflective substrate coated with a submicrometric dielectric spacer. The metasurfaces rely on a cornerstone geometry of nanophotonics referred to as nanoparticles on reflective substrates, which are easy to fabricate and offer manifold optical resonances passively or dynamically tunable by varying the film thickness or permittivity. The researchers demonstrated a remarkable iridescence phenomenon with only two distinct colors using solar simulation. They found that these color transitions were not classical iridescence resulting from thin-film interferences combined with diffuse reflection added by roughening the film surfaces. Instead, they discovered that diffuse colors and their gradual variations had very little to do with those produced by the specular iridescence of the same thin SiO2 layer. The metasurfaces were fabricated by dip-coating a SiO2/Si wafer with a colloidal monolayer of silver nanocubes. The study gathered experimental results for samples obtained with moderate silver nanocube densities and SiO2 layer thicknesses ranging from 0 nm to 700 nm. The nanoparticle density had little impact on appearance but reinforced diffuse brightness without changing hue. Overall, this work highlights uncommon iridescences that differ from those classically observed with natural nanostructures or thin-film interferences. The interpretation paves the way towards the design of easy-to-make and universal building blocks with a large resilience to fabrication imperfections, and great potential for innovative coatings and fine-art applications.