Metasurface structural colour in simple words

21 September 2017

Reflection, transmission, absorption, scattering and diffraction are the typical optical phenomena that occur when light (visible) interacts 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 our surroundings. That means manipulation of the light-matter interaction by engineering the outer surface of the object induces different colours. This is indeed the basics of the 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 reaches our eyes by manipulating the structure in metasurfaces and hence make a 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 the silver metal of a certain size atop of silver mirror leads to 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 the former case is peaked at the green part of the spectrum while the blue wavelengths are completely reflected in the latter case. The concept of metasurface structural colour nowadays attracts the attention of scientists around the world because it could enable printing on a smaller scale and above all free designers from using toxic colourant pigments.

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