# Structural Color 3D Printing By Shrinking Photonic Crystals

## TL;DR

This paper presents a novel 3D printing method for photonic crystals with sub-100 nm features, enabling full-color microscopic objects and advancing nanoscale color printing technology.

## Contribution

Introduces a new technique to produce 3D photonic crystals with significantly reduced lattice constants, allowing for microscopic, full-color 3D printing of complex structures.

## Key findings

- Achieved 5x reduction in lattice constants to ~280 nm.
- Printed the first multi-color microscopic model of the Eiffel Tower.
- Demonstrated control over photonic band structures matching experimental results.

## Abstract

The rings, spots and stripes found on some butterflies, Pachyrhynchus weevils, and many chameleons are notable examples of natural organisms employing photonic crystals to produce colorful patterns. Despite advances in nanotechnology, we still lack the ability to print arbitrary colors and shapes in all three dimensions at this microscopic length scale. Commercial nanoscale 3D printers based on two-photon polymerization are incapable of patterning photonic crystal structures with the requisite ~300 nm lattice constant to achieve photonic stopbands/ bandgaps in the visible spectrum and generate colors. Here, we introduce a means to produce 3D-printed photonic crystals with a 5x reduction in lattice constants (periodicity as small as 280 nm), achieving sub-100-nm features with a full range of colors. The reliability of this process enables us to engineer the bandstructures of woodpile photonic crystals that match experiments, showing that observed colors can be attributed to either slow light modes or stopbands. With these lattice structures as 3D color volumetric elements (voxels), we printed 3D microscopic scale objects, including the first multi-color microscopic model of the Eiffel Tower measuring only 39-microns tall with a color pixel size of 1.45 microns. The technology to print 3D structures in color at the microscopic scale promises the direct patterning and integration of spectrally selective devices, such as photonic crystal-based color filters, onto free-form optical elements and curved surfaces.

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Source: https://tomesphere.com/paper/1905.05913