Reflection, transmission, absorption, scattering and diffraction are the typical optical phenomena which occur when light (visible) interact with an object. In many cases, the absorption of the incident light by the medium is dominant however reflection, diffraction and scattering are the main cause of the colour that our eyes percepts from surrounding. That means manipulation of the light matter interaction by engineering the outer surface of the object induce different colour. This is indeed the basics of structural colour base on metasurface (or metamaterials).
It is already known that metamaterials optical properties can be tuned by changing the geometry and arrangement of their building block. So, it is possible to adjust the amount of the colour that reach to our eyes by manipulation of the structure in metasurfaces and hence make new colour.
This is generally done by altering the size of the components of the metasurfaces (known as meta-atoms), re-arrangement of the surface patterns as well as changing the material constituents of the metasurface.
For instance, if silver metal of certain size atop of silver mirror leads in green colour, enlarging the size of the features (e.g. meta-atoms) can result in blue colour (see the illustration above). This is because the reflection of the light in former case is peaked at green part of spectrum while the blue wavelengths are completely reflected in latter case. The concept of metasurface structural colour is nowadays attracts the attention of scientists around the world because it could enable printing in smaller scale and above all it free designers from using of toxic colorant pigments.
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