Color Tunable, Lithography-Free Refractory Metal-Oxide Metacoatings with a Graded Refractive Index Profile

The refractory metal-oxide semiconductors are an overlooked platform for nanophononics that offer alloys with high melting points and tunable optical constants through stoichiometry changes and ion intercalation. We show that these semiconductors can form metamaterial coatings (metacoatings) made from a set of highly subwavelength, periodic metal- oxide layers (<= 20 nm) with a varying and graded refractive index profile that includes a combination of high and low refractive indices and plasmonic layers. These metacoatings exhibit vibrant, structural color arising from the periodic index profile that can be tuned across the visible spectrum, over ultralarge lateral areas through bottom-up thermal annealing techniques.

Automated summary

Refractory metal-oxide semiconductors, with their high melting points and tunable optical constants, are a neglected platform for nanophononics. We demonstrate that these semiconductors can form metacoatings made of highly subwavelength, periodic metal-oxide layers with a varying refractive index profile. These metacoatings exhibit vibrant structural colors and can be tuned across the visible spectrum through thermal annealing techniques.