Engineering Chirality in Semiconductor Nanoclusters

Researchers at Cornell University have developed a method to convert symmetric semiconductor particles into chiral materials—intricately twisted structures that produce films with enhanced light-polarization control. The findings have potential applications in displays, sensors, and optical communication devices that rely on polarization control.

Chiral materials are distinguished by their ability to rotate polarized light. One approach to achieving this effect is exciton coupling, where light excites nanomaterials, forming excitons that interact and exchange energy. Traditionally, exciton-coupled chiral materials have been based on organic, carbon-based molecules. However, precise control over nanomaterial interactions has made it challenging to create such materials using inorganic semiconductors, which offer greater stability and tunable optical properties.

To address this challenge, researchers in Richard D. Robinson's lab, an Associate Professor of Materials Science and Engineering at Cornell Engineering, utilized "magic-sized clusters" composed of cadmium-based semiconductor compounds.

Unlike conventional nanoparticles, which exhibit continuous size variation, magic-sized clusters exist only in discrete, uniform sizes. Previous studies by the Robinson Group demonstrated that when these nanoclusters were processed into thin films, they exhibited circular dichroism, a key characteristic of chirality.

Circular dichroism means the material absorbs left-handed and right-handed circularly polarized light differently, like how screw threads dictate which way something twists. We realized that by carefully controlling the film’s drying geometry, we could control its structure and its chirality. We saw this as an opportunity to bring a property usually found in organic materials into the inorganic world.

Richard D. Robinson, Study Senior Author and Associate Professor, Materials Science and Engineering, Cornell Engineering

Using meniscus-guided evaporation, researchers induced linear nanocluster assemblies to twist into helical structures, forming homochiral domains several square millimeters in size. The resulting films exhibited a light-matter interaction strength nearly two orders of magnitude higher than previously recorded for inorganic semiconductor materials.

I’m excited about the versatility of the method, which works with different nanocluster compositions, allowing us to tailor the films to interact with light from the ultraviolet to the infrared. The assembly technique imbues not only chirality but also linear alignment onto nanocluster fibers as they deposit, making the films sensitive to both circularly and linearly polarized light, enhancing their functionality as metamaterial-like optical sensors.

Thomas Ugras, Doctoral Student and Research Lead, Applied and Engineering Physics, Cornell University

These findings have potential applications in holographic 3D displays, room-temperature quantum computing, ultra-low-power electronic devices, and non-invasive blood glucose monitoring. Additionally, the study provides insights into the natural formation of chiral structures, such as DNA, which could inform future research in biological and nanotechnological systems.

“We want to understand how factors like cluster size, composition, orientation, and proximity influence chiroptic behavior. It’s a complex science, but demonstrating this across three different material systems tells us there’s a lot to explore, and it opens new doors for research and applications,” said Robinson.

Future research, according to Robinson, will concentrate on expanding the method to other materials, like quantum dots and nanoplatelets, and improving it for large-scale production processes that cover devices with thin layers of semiconductor materials.

The National Science Foundation provided the majority of the funding for the study. Data collection was supported by a Cornell Graduate School Research Travel Grant. The work was conducted in part at the Diamond Light Source in the United Kingdom and at the Cornell Materials Research Science and Engineering Center and the Materials Solutions Network at CHESS (MSN-C), a sub-facility of the Cornell High Energy Synchrotron Source supported by the Air Force Research Laboratory.

Journal Reference:

Ugras, J., T., et al. (2025) Transforming achiral semiconductors into chiral domains with exceptional circular dichroism. Science. doi/10.1126/science.ado7201