Structural Colors on Al Surface via Capped Cu-Si₃N₄ Bilayer Structure

Area of Science:

• Materials Science
• Optics
• Nanotechnology

Background:

• Tunable structural colors are crucial for applications in mobile devices, artwork, and color filters.
• Metal-Insulator-Metal (MIM) designs offer a pathway to systematically control structural colors.

Purpose of the Study:

• To develop and characterize a MIM design for tunable structural colors.
• To evaluate the effectiveness of various capping layers in protecting the color-generating structure.

Main Methods:

• Fabrication of a MIM structure using Copper (Cu) and Silicon Nitride (Si3N4) on an Aluminum (Al) substrate.
• Systematic tuning of structural colors by altering the thickness of the top metal and insulator layers.
• Application and evaluation of capping layers (SiO2, LPSQ, PMMA, ProtectaClear) for surface protection.

Main Results:

• Vivid structural colors (brown, orange, blue, violet, magenta, cyan, green-yellow, yellow) were successfully printed by controlling layer thicknesses.
• ProtectaClear and LPSQ coatings demonstrated minimal angle dependency and protected the Cu surface from humidity without color degradation.
• Bilayer coatings (PMMA/SiO2, ProtectaClear/SiO2) provided enhanced protection against humidity and corrosion.

Conclusions:

• The MIM design enables systematic tuning of structural colors through precise control of layer thicknesses.
• Selected capping layers, particularly ProtectaClear and LPSQ, effectively protect the structural color without compromising optical performance or angle dependency.
• The observed colors are attributed to thin-film interference, with no evidence of plasmonic effects.