Conjugated Energy Transport and Hot Carrier Diffusion in 2D Transition Metal Dichalcogenides: Novel Characterization toward Fundamental Understanding

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Two-dimensional transition metal dichalcogenides (TMDs) are materials that have an extremely small thickness (down to a few atoms level). They have broad applications including flexible circuits, sensors, and low power transistors. Their thermophysical properties and energy transport capability directly determine their performance and durability. Also, their electron transfer rate is a property that directly determines device functionality. This project uses ultrafast lasers and a continuous laser to excite and probe the molecular vibrations modes (Raman spectroscopic signal) of TMDs, and use such signals to distinguish and characterize the thermophysical properties, electron transfer rate, and interface energy transfer capability. The outcome of the project should establish the critical knowledge base needed in TMDs structure tailoring, device design, and thermal optimization. Furthermore, the project integrates research activities into education via classroom teaching and new class module development, fosters minority student research training, and stimulates research interests of K-12 students by various outreach activities including science fair, lab tour, and providing high-school teacher research experience.The goals of this project are to conduct further deployment of a novel energy transport state-resolved Raman to characterize hot carrier diffusivity, phonon thermal conductivity, interface thermal resistance for supported TMDs, and electron-hole nonradiative recombination coefficient for monolayered TMDs. The project investigates the effect of physical structure on the three transport processes: hot carrier diffustion, in-plane phonon transport, and cross-interface energy transport (for supported TMDs), studies the effect of substrate on properties, and explores the effect of temperature (70 K to 850 K) on properties as well. This represents the first and high precision consideration of hot carrier transport and radiative electron-hole recombination in 2D materials. This project significantly promotes the field of defect engineering in 2D TMDs, and provides frontier perspective on the challenges and opportunities in this emerging field.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.