Researchers Discover Novel Method for Creating Colloidal Diamonds

Colloidal diamonds - stable, self-assembled material with promising applications in light-related technologies - can now be fabricated, decades after its concept was first developed in the 90s.

Researchers from the New York University Tandon School of Engineering, led by engineering professor David Pine, have developed a novel method for reliable self-assembly of colloidal particles in a diamond lattice formation. This discovery could potentially create a way for cost-effective and scalable production of colloidal diamonds.

The method for fabricating these sought-after materials and the results of their studies was published in the journal Nature, September 24.

Fabricating Colloidal Structures

According to a press release from the New York University Tandon School of Engineering, the team behind the new method for creating colloidal diamonds, including Pine, lead author and postdoc researcher Mingxin He, and associate professor Stefano Sacanna, have been at work with colloids and their possible structures for decades.

Colloids used in the study are spherical materials orders of magnitude smaller than the width of a strand of human hair. These can be arranged in crystalline shapes with the resulting structure depending on the connection between these colloids. For colloidal diamonds to be used for applications requiring a photonic bandgap - a dielectric profile in between colloids that prevent light, or specific frequencies of it, to propagate through the material - proponents of the research also noted a cubic diamond structure. However, they indicated that self-assembly in colloidal diamonds is "challenging."

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Since a diamond lattice structure requires particles to exhibit tetrahedral coordination between colloids, previous attempts focused on self-assembling colloids with "tetrahedral sticky patches" were often restricted by the need for the patch spheres to select the staggered orientation in keeping tetrahedral bonds.

The existing process attaches colloids using DNA strands to connect them. When submerged in a liquid bath, colloidal particles collide and cause the DNA strands to hold each colloid in a particular direction. Depending on the location of the DNA on the colloid surface, researchers can limit the direction at which bonds form and create complex structures.

Achieving the Rare Photonic Bandgap

"There's been a great desire among engineers to make a diamond structure," said Pine in the NYU Tandon release. He noted that other teams working toward the same goal have "given up on it," adding that his team might be the last one still working on colloidal diamonds.

"I think the publication of the paper will come as something of a surprise to the community," Pine commented.

Proponents of the paper, including former New York University Tandon postdoc Etienne Ducrot, now with France's Paul Pascal Research Center; and Gi-Ra Yi from South Korea's Sungkyunkwan University, have observed that with a steric interlock mechanism, they can spontaneously generate the required staggered bonds needed for a colloidal diamond.

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Instead of building these structures through nanomachines, which will attach DNA strands at precise locations, the novel method will allow the colloid to form the required configuration by itself. Proponents of the research also demonstrated that the colloidal diamonds remain stable even outside their liquid bath.

Dr. Evan Runnerstrom, Army Research Office program manager, said that Dr. Pine's demonstration of the colloidal diamond lattice would "unlock new research and development opportunities" in the field of defense tech, through their 3D photonic crystals.

Among the potential applications of colloidal diamonds include high-efficiency lasers with reduced weight and energy requirements, precise control of light, or management of optical signatures.