DTU Nanotech paper in Science Advances

Tuesday 09 May 17

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Anders Kristensen
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DTU Health Tech
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The paper “Resonant laser printing of structural colors on high-index dielectric metasurfaces” by X. Zhu, W. Yan, U. Levy, N. A. Mortensen, and Professor Anders Kristensen from DTU Nanotech was recently published in Sciences Advances, 05 May 2017, Vol 3, No 5, e1602487, DOI: 10.1126/sciadv.1602487.

The paper describes how unlike colours produced by chemical dyes or pigments, structural colours rely extensively on the physical geometry and materials and the colours will not fade over time (the way ink does). The researchers behind the article have constructed a so-called meta-surface comprising 60 nanometers high columns of plastic. The surface is coated with a layer of germanium, which is only 35 nanometers thick. Semiconductor material lies on top of the columns. These coloured metasurfaces are ultrathin, flexible and can be laser printed for colours without ink. 

Only a single material, Germanium, is involved here, which promises easy recycling for the future products. Small disks of the semiconductor material germanium can absorb a certain part of the colour spectrum, thus reflect the other colour spectrum. The idea to change these structural colours is simply to change the geometry by a laser, for instance, which may warm up a disk and melt it into a sphere or even ablate the sphere away. Small spheres can absorb another certain part of the colour spectrum and reflect a different colour than disks. By this means, it is possible to adjust the laser's strength so that the disks melt more or less, thus realising a group of colours. Because the heating process is only applied to nanoscale materials, and only the single disk in the center of the laser spot can absorb the laser energy efficiently and warm up to its melting point, the neighboring disks absorb less energy which is not enough to change the geometry. Thus, it’s possible to change the colours on the single disk level, which gives a resolution over 100.000 dpi. The printed structure colours may replace any ink based colour pinting products. They do not fade over time when exposed to sunlight. 

The research on which the paper is based is a collaboration between DTU Nanotech and DTU Fotonik.

Download the article here:

 

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26 AUGUST 2019