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

该奖项支持研究克服二维材料制造中晶体质量和横向尺寸相互排他性的挑战。二维材料是原子薄膜，其特性可以彻底改变低功耗电子，生物检测，多功能复合材料和能量存储应用，为美国社会和经济带来重要利益。这些应用的障碍是，当生长在大尺寸时，二维材料的结晶度很差，传统的热处理不能改善结晶度，因为材料通常耐高温。该奖项允许研究一种完全不同的方法，在这种方法中，二维材料在大面积生长，最初质量很低，然后通过电气和机械处理的结合大大改善。这是一个多学科的方法，培养研究生在纳米制造，材料科学和机械工程的前沿方面。该项目让本科生、妇女和代表性不足的少数民族学生参与研究，以更好地培养未来多样化的劳动力。该奖项旨在研究通过原子层或脉冲层沉积在大面积上制造原子薄二维（2D）材料。生长的纳米晶通常结晶度较低。电子风力和机械应力的结合提高了结晶度。电子在缺陷和晶界处转移其动量，从而在较低温度下赋予前所未有的原子/缺陷迁移率。机械应力的作用是加速电退火。假设缺陷周围的应力场可以强化局部应变能，这是结晶和晶粒长大的驱动力。建立了基于反应经验键序势的计算模型，并将电子风力传递给单个原子，以指导实验研究。在透射电子显微镜下进行实验，了解超薄膜的合成和机电退火。原位显微镜显示了从低质量的非晶相到高结晶态的转变。研究表明，采用一种新型的电机械处理方法可以代替传统的热处理方法获得高结晶度的二维原子层材料。该研究还探讨了该技术的规模，通过在高残余应力涂层的衬底上进行晶圆级合成，然后进行电退火。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.