Wafer-Scale Manufacturing of Two-Dimensional Anisotropic Nanomaterials by Chemical Vapor Deposition

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Anisotropic nanomaterials are materials that form with molecular order in a two-dimensional (2D) atomically-thin topography. Recent discoveries have shown that these materials exhibit extraordinary physical and chemical properties, such as high electron mobility, high temperature superconductivity, and thermally stable polarized excitons. They have the potential to dramatically impact technological advances, which can affect many industrial sectors, from national defense (sensors and detectors) to energy conversion (solar cells and hydrogen generation), and communication (high speed electronics). But manufacturing atomically-thin nanomaterials reproducibly and economically is difficult. Current manufacturing techniques do not allow for synthesis with atomic precision and tend to fabricate materials that are highly disordered. This award supports fundamental research to develop a robust manufacturing process to meet this challenge and unleash the promised power of anisotropic nanomaterials. These materials are grown on solid templates by chemical vapor deposition (CVD). If successfully manufactured, these materials can function as building-blocks in complex device architectures for a variety of applications, thus translating fundamental scientific discoveries into useful products. Additionally, knowledge generated by this project can be extended to the manufacturing of many ultra-thin coatings. This project greatly enhances the teaching and education of the next generation of engineers and scientists. In an active research environment, high school, undergraduate and graduate students are trained, with a significant effort given to involving women and underrepresented minority groups. This project establishes the thermodynamics and kinetics of the nucleation and growth of two-dimensional (2D) anisotropic nanomaterials, such as ReS2, GaTe, ZrTe3, and NbS3. The method involves designing the surface morphology and chemistry of solid templates so that the 2D anisotropic nanomaterials grown on them are defect free and have highly oriented chains required for practical applications. The project investigates the role played by the substrate, surface chemistry, and vacancy defects in large-scale manufacturing. The approach is to use precursors in vapor form and react them at low temperatures, making it low-cost and easy to scale. It identifies a set of conditions, such as surface characteristics, required to achieve high crystallinity and full coverage growth across wafers up to 4 inches. Wafer scale characterization tests help to correlate growth parameters to thickness, stoichiometry, and anisotropy uniformity across the wafer, and guide the growth parameterization efforts. Unlike commonly used powder evaporation CVD for laboratory-scale 2D nanomaterial fabrication, this project utilizes a gas-CVD technique involving CVD showerheads. This allows the independent control of precursor concentrations, minute control over nucleation density, flow rates, gas streamlines, and temperature profiles which is ideal for industrial-scale manufacturing.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.