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

该奖项支持研究，以克服在二维材料制造中晶体质量和横向尺寸相互排斥的挑战。二维材料是原子薄膜，具有革命性的低功耗电子、生物检测、多功能复合材料和能量存储应用，有望为美国社会和经济带来重要好处。这些应用的障碍是，当生长尺寸较大时，二维材料的结晶度很差，而且传统的热处理不能提高结晶度，因为这些材料通常耐高温。这一奖项使得研究一种完全不同的方法成为可能，在这种方法中，一种二维材料在一大片面积上种植，最初质量较低，然后通过电气和机械处理的组合得到极大的改善。这是一种多学科的方法，培养研究生在纳米制造、材料科学和机械工程的尖端方面。该项目邀请本科生、女性和少数族裔学生参与研究，以更好地培训未来多样化的劳动力。该奖项调查通过原子层或脉冲层沉积在大范围内制造原子薄的二维(2D)材料。生长的纳米骨通常结晶度较低。在电子风力和机械应力的共同作用下，结晶度得到提高。电子在缺陷和晶界传递它们的动量，从而在较低的温度下提供前所未有的原子/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增强局部应变能，而局部应变能是晶化和晶粒长大的驱动力。建立了基于反应性经验键级势和单个原子所受电子风力的计算模型来指导实验研究。在透射电子显微镜内进行了实验，以了解超薄膜的合成和机电退火法。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，通过一种新型的电气和机械处理方法代替传统的热处理方法，可以获得结晶度较高的二维原子层材料。这项研究还研究了通过在涂有高残余应力的衬底上进行晶片规模的合成，然后进行电退火来扩大这项技术的规模。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.