Materials with a tailored color are important not only for aesthetic purposes but also for a variety of devices such as optical switches, displays, or camouflage. These applications also often require the color to be independent of the angle of illumination or the angle of view. A very flexible approach to achieve such features consists in harnessing strong optical interference effects in metal-dielectric nanomaterials. By tailoring the material structure at the nanoscale, optical interference can be controlled to induce a perfect absorption of light in selected spectral regions. This enables tailoring the spectrum of the reflected light, and thus the material color. Based on this idea, it is remarkable that an angle-independent color can be obtained with only a thin dielectric film on a low reflectivity metal, and that such color can be tailored by simply varying the dielectric thickness. This is exemplified here by Theodore Letsou and coworkers, who baked nickel and titanium samples to form a thin oxide layer at their surface. By controlling the baking time, they tuned the oxide layer thickness to achieve different colors from beige to blue.
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