Nanomanufacturing of Atomically-Uniform Two-Dimensional Materials over Large Areas

This award supports research to overcome a challenge of mutual exclusiveness of the crystalline quality and lateral size in the manufacture of two-dimensional materials. Two-dimensional materials are atomically thin films with properties that can revolutionize low-power electronics, biological detection, multi-functional composites and energy storage applications that promise important benefits for the US society and economy. The roadblock to these applications is that, when grown in large size, the two-dimensional material's crystallinity is poor and conventional heat treatment does not improve the crystallinity because the materials are typically resistant to high temperatures. This award enables the investigation of a fundamentally different approach, where a two-dimensional material is grown over a large area with initially low quality, which is then greatly improved through the combination of electrical and mechanical treatments. This is a multi-disciplinary approach, which trains the graduate students in cutting edge aspects of nanomanufacturing, materials science and mechanical engineering. The project involves undergraduate, women and under-represented minority students in research to better train the diverse work force of the future.

This award investigates the manufacture of atomically thin two-dimensional (2D) materials over large areas by atomic layer or pulsed layer deposition. The as-grown nanosteets are usually of low crystallinity. The crystallinity is enhanced with a combination of electron wind force and mechanical stress. The electrons transfer their momentum at the defects and grain boundaries to impart unprecedented atomic/defect mobility at lower temperatures. The role of mechanical stress is to accelerate the electrical annealing. The hypothesis is that the stress field around the defect can intensify the local strain energy, which is a driving force for crystallization and grain growth. Computational models, based on reactive empirical bond-order potential with the electron wind force imparted to individual atoms, are developed to guide the experimental research. Experiments are performed inside the transmission electron microscope to understand the synthesis of ultra-thin films and electro-mechanical annealing. The in-situ microscopy reveals the transformation from a low quality amorphous phase to a highly crystalline state. The research demonstrates that high crystallinity 2D atomic layer materials can be achieved by a novel electrical and mechanical treatment instead of conventional heat treatment. The research also investigates scaling up of this technique by wafer-scale synthesis on a substrate coated for high residual stress followed by electrical annealing.

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.