Scientists have created a way to fabricate a complex structure, previously found only in nature, to open up new ways to manipulate and control light.
According to a new study by researchers at the University of Birmingham, the structure, which occurs naturally in the wing scales of some species of butterflies, can act as a photonic crystal. It can be used to control light in the visible range of the spectrum, for laser applications, sensors, as well as solar energy harvesting devices.
Their computational study was published in Advanced materialsshows that the complex thyroid architecture can be self-assembled from tailored colloidal particles in the range of hundreds of nanometers.
The thyroid gland is usually known for its curved surface, which divides the space into two interlocking ducts. Each of these channels can contain a grid representation of vertices associated with a three-way connection and screws through space in a specific direction, right or left. This twist causes each web to spiral—mirror images cannot be superimposed on each other, like left and right hands. This is important because chirality imparts additional optical properties to a photonic crystal.
However, reproductive symmetry is lost when the two oppositely conducting networks are together in the form of a paired thyroid structure. This happens in some artificial systems.
In this work, the team of researchers first presented a single gyro-network structure built from colloidal spheres as a target for self-assembly—the natural way of building structures—before laying out design principles for fabricating this chiral crystal structure in a computer simulation. .
Dr Angela Demetriado, co-author from the College of Physics and Astronomy, said: “This is an exciting new method for fabricating photonic nano-media with exceptional, tailored optical chiro-properties, with tremendous control over their properties.”
Until now, the focus of self-assembled colloidal photonic crystals has been mostly on diamond structures. The self-assembly of colloidal diamond presents a number of challenges, including the requirement to choose a cubic shape over its hexagonal counterpart for its practical applications as photonic crystals in optical devices.
The novel approach developed in this work involves patchy domains, which have a patterned surface designed to encode target structure information – a single colloid thyroid. The textured parts of the surface are sticky to bring the particles together to form the lattice structure. In addition, the work shows that a single colloidal thyroid also has interesting optical properties by virtue of its anisotropy, which the structure of diamond lacks.
Dr Dwipayan Chakrabarti, corresponding author from the University of Birmingham’s School of Chemistry, said: “To the best of our knowledge, this is the first report of direct self-assembly of single thyroid colloid structures from designed building blocks. We hope that our new approach will stimulate further investigations in the field of colloidal self-assembly.” , and especially experimental efforts to build on this exciting development.”
This excitement is echoed by Stefano Sacana, a NYU professor with world-leading expertise in synthesizing colloids and self-assembling new materials, who was not involved in this study. He said, “With their work, Chakrabarti and colleagues bring to the attention of the colloidal self-assembly community an exciting new target. Using only spheres with a clever incomplete design, their bottom-up pathways to colloidal thyroid structures pave the way for a new generation of experimentally achievable photonic crystals.” .
