Chiroptical properties of patterned nanocrystal solids

Chiral materials and objects are central to our lives. Biomolecules and pharmaceuticals are synthesized in specific geometries to enable selective and targeted interactions, while objects such as screws and rotors convert rotational motion to linear force. However, there are very few examples of chiral materials with nanoscale or mesoscale dimensions. Materials at these length scales are particularly important for interactions with polarized light. Chiral molecules absorb different polarization states of light to different extents, the effect is orders of magnitude stronger in appropriately designed nanostructures. The detection of polarized light is integral to sensors and imaging systems, and the generation of circularly polarized light is essential to the development of stereoscopic displays, of anti-counterfeiting security, and of quantum optical circuits. This project focuses on the fundamentals of the design, fabrication, and characterization of nanostructured materials to control the absorption and emission of circularly polarized light by creating new nanostructures comprised of light-emitting nanocrystals. The project also advances the fields of nanopatterning and fabrication. The research conducted will train students in photonics, nanotechnology, and materials characterization. As part of this project, the PI will leverage online education modalities for a senior capstone course and conduct educational studies in the classroom. The PI will also engage K-12 students with advanced technology and collaborate with a local visual artist.

Chiral nanostructures and metasurfaces exhibit orders-of-magnitude stronger interactions with circularly polarized light than their molecular counterparts. Many technological applications, however, would benefit from the controlled generation of circularly polarized photoluminescence. This project creates and characterizes metasurfaces comprised of both plasmonic nanostructures and tailored assemblies of semiconductor nanocrystals, where the nanocrystals are patterned into hierarchical structures using direct-write electron beam lithography. The experiments are complemented by full-field electromagnetic simulations to understand the interactions between the nanocrystals and the plasmonic nanostructures. By tailoring the position and shape of the semiconductor nanocrystals, these multi-material metasurfaces offer both enhanced angular control and enhanced degrees of circular polarization. The understanding gained from these studies contributes to the development of stereoscopic displays, of anti-counterfeiting strategies, and of photonic circuits. Students gain experience in diverse techniques, including nanocrystal synthesis, lithographic patterning, optical characterization, and electromagnetic simulations. The project also studies inclusivity in undergraduate courses and the role of exam anxiety, trains undergraduate students in the senior capstone design course, engages K-12 students in activities related to light polarization, and develops art installations in collaboration with a local visual artist that allow the broader community to experience light-matter interactions at a larger scale.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.