Carbon nanotubes are small tubes with walls that are a single atom thick and diameters that can be a hundred thousand times smaller than a strand of hair. In a perfect nanotube, each carbon atom is bound to 3 other atoms, forming a hexagonal lattice. Defects can be introduced in the lattice by attaching small organic molecules to the outside of the tube such that a few atoms in the lattice are bound to 4 carbons, instead of 3. These quantum defects attract charge carriers moving along the tube, enabling them to fluoresce brightly. With support from the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry, Professor YuHuang Wang at the University of Maryland College Park and his students are using super-resolution microscopy techniques to study individual fluorescent defects. Their discoveries could have important implications for emerging technologies in chemical sensing and quantum information science. Understanding the nanochemistry of quantum defects may enable the precise synthesis of a whole new family of quantum emitters, and make it possible to experimentally probe defects at the single defect limit as well as chemical events that are otherwise difficult to capture. This research has potential for extending applications in nanochemistry, photophysics, quantum theory, materials engineering, optoelectronics, biological imaging, and quantum science and engineering offering increased global and economic competitiveness for the United States. The research provides a unique opportunity to develop engaging outreach demos and involve undergraduate students from under-represented groups in cutting-edge research.
Professor Wang and his students design and synthesize sp3 quantum defects by covalently attaching selected alkyl or aryl functional groups to semiconducting carbon nanotube model systems. Excitons -- electron-hole pairs each carrying a quantum of excitation energy -- are efficiently harvested by the defects producing bright emission that encodes chemical information at the defect site. The team is exploiting this intriguing property and advancing a super-resolution hyperspectral imaging technique in the shortwave infrared to study the spectroscopic properties of these synthetic defects at the single defect limit. Furthermore, the dependence of the emission spectrum on the nature of the chemical defect is being used to watch the breaking and formation of bonds in model chemical reactions involving aminoaryl substituents. The team is also characterizing functionalization patterns of sp3 quantum defects at the high-density limit and studying how sp3 defect chemistry may propagate on the sp2 lattice of low-dimensional carbon materials.
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