Elemental tellurium is a fascinating chiral semiconductor with high refractive index, excellent infrared transmission and strong spin orbit coupling, and has great potential for photonic and spintronic devices. The as-synthesized tellurium crystals, however, are typically racemic mixtures of chiral domains. In this work, we designed a simple and scalable optical imaging method based on polarization resolved nonlinear harmonic generation to identify the chirality in tellurium nanowires, which correlates with the structural helicity of the wires observed in transmission electron microscope. The ability to quickly identify chiral structures and domain boundaries may enable more studies on their novel transport properties. This work was performed in collaboration with Pettes group in Los Alamos National Laboratory and published in Nanoscale.

Valleytronics, a new and potentially energy-efficient form of computing hardware, was previously thought to be incompatible with perovskite, a promising energy harvesting semiconductors. Having both functionalities in one single-crystal material is beneficial for monolithically integrated information technology in industrial fabrication. In this work, we identified the necessary atomic lattice symmetry for valleytronics in newly synthesized ultrathin perovskite with nonlinear optical spectroscopy. The finding of entirely different symmetry properties from bulk materials led to the discovery of robust optical valley memory effect, which is surprising at the first glance but understandable from first principle calculation. This collaborative work with Lou group at Rice MSNE and Qian group at TAMU MSE is now published in Advanced Materials. Read more at Rice News.

Light-controlled polymerization has wide applications in additive manufacturing and medicine, but the common catalysts work under UV-blue light, which does not penetrate beyond the surface of the materials or tissues, and may have negative physiological effects. In this work, we demonstrated that perovskite nanocrystals are excellent nonlinear photocatalyst that can be activated with near-infrared light. The giant two-photon absorption coefficient of the nanocrystal, compared with dye molecule catalysts, allows efficient volumetric reaction. Applying a special type of polymerization, PET-RAFT, we showed that the entire solution volume of 1 mL contains polymer chains with highly uniform molecular length (dispersity of 1.07 is very close to unity), which is challenging for conventional laser direct writing. This collaborative work with Egap group at Rice MSNE is published in ACS Macro Letters.

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