Semiconductor nanocrystals, also known as quantum dots (QDs), are emerging as a class of unique materials due to their unparalleled features: a compact size, broad excitation band, large absorption cross section, tunable narrow/symmetric emission profile, superior photostability and solution processability. Research in the Chen laboratory focuses on developing novel QD-based materials ranging from nanoscopic to macroscopic scales and characterizing and elucidating their chemical and physical properties for energy, optical, optoelectronic, catalysis and biological applications.

Synthesizing Anisotropic QD NCs with Exquisite Control: The promise of nanoscience cannot be fully realized without robust and reliable synthetic methods to prepare nanomaterials with exquisite control of size, shape, surface and compositions. The uniformity of synthesized nanocrystals (NCs) critically impacts their individual properties and their assembly into high-order architectures. There were few methods for controlled synthesis of anisotropic NCs, thus constraining their exploration as building blocks for superstructural assembly, despite obvious applications. In Chen lab, we are exploring methods to balance reaction kinetics and thermodynamics to generates anisotropic NCs of high quality and uniformity. We are applying the discovered principles to develop a suite of methodologies that enable controlled fabrication and functionalization of high-quality anisotropic QD-based NCs using uniform NCs and/or QDs as seeds. Importantly, ready access to uniform, anisotropic NCs with exquisitely controlled morphology, composition, and surfaces facilitates exploration of their assembly into higher-order superstructural materials for various applications.

Assembling NCs into Programmable Superstructural Materials: Organization of nanocrystals (NCs) into larger superstructures is a promising approach for integrating the useful properties of single NCs into macroscopic forms relevant in technology. These NC superstructural materials possess order on multiple length scales with promising and unique functionalities. However, preparing such functional materials requires exquisite structural control from the nano- to macroscopic levels. My research aims to design these materials by developing syntheses of size, shape and surface tailored quantum dot (QD) NC building blocks and exploring methods for their assembly into atomically precise, superstructural nanomaterials. Correlating nanomaterial properties and function to NC chemical composition, atomic arrangement, structural configuration, and interparticle interactions reveals design principles for the next generation of functional materials. These materials are endowed with novel, programmable properties that fully exploit the individual particle as well as the hierarchical superstructure. By using chemical and physical tools, we are trying to explore and understand the novel and enhanced collective properties from the near-field coupling to long-range interactions that occurs between NC neighbors inside the superlattices. 

Tuning Functionalities and Morphologies of NCs and Superstructures: Armed with the ability to form entirely new types of NC-superstructural materials, we evaluate how to tailor these materials to generate novel and important properties. Until recently, structure-property studies of these systems have been restricted to “confined” nanostructured materials, in which nanoscopic properties of the building blocks remain intact. In our laboratory, we have been developing chemical and physical methodologies to finely tune NCs and their superstructures to enhance near field interactions between particle neighbors. By developing and combining in situ characterization tools, we are exploring methodologies with capabilities to simultaneously probe structure (from atomic to micron scales) and properties (e.g., optical and mechanical properties) in real time. We aim to access quick optimization of the nanomaterials that represents one ideal confined-but-connected structures to reach the best performance of their desired properties. The optimized nanomaterials show promise for a range of technological applications including solar energy harvesting devices, photodetectors, photocatalysts, lighting and displays.

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