CAREER: Experimental Investigation of Plasticity at Nano-scale via in-situ Mechanical Deformation

技术：设备的功能直接取决于结构完整性和机械稳定性，因此有必要了解和预测材料在降维时的机械性能。屈服和断裂强度已经被发现偏离了经典的力学定律，因此不能再从整体响应或文献中推断出来。不幸的是，现有的为数不多的用于评估这种规模的机械性能的实验技术是不够的，不容易获得，而且通常局限于薄膜。为了设计可靠的设备，迫切需要对纳米级的机械响应有一个基本的了解；剩下的问题是，当仪器文物被移除时，材料是否真的更坚固，如果是，那么为什么以及如何移除。这个项目研究了纳米晶体在特定的机械变形下的基本塑性机制和缺陷演化(具体地说，位错)。实验确定的应力-应变关系将通过原位扫描电子显微镜观察和微观结构表征得到加强，这将有助于开发与微观流动应力响应一致的全面物理缺陷模型。该项目首次提出了一个统一的计划，将独特的纳米级样品制备技术与新的原位机械测试能力和后变形透射电子显微镜相结合。这个项目将利用PI在使用聚焦离子束(FIB)作为纳米级样品制造和随后的操纵以及透射电子显微镜横截面制备的独特工具方面的专业知识。在这个项目中，跨科学学科的边界合并将是至关重要的，因为要在纳米尺度上充分解决可塑性问题，材料科学、显微镜和机械界必须共同努力。这项研究将跨越长度尺度，努力识别和表征尺寸限制在纳米尺寸的晶体材料变形过程中发生的位错过程。非技术性：随着许多纳米级设备深刻地影响着我们的日常生活，这个项目为自己提供了一个产生更广泛影响的完美机会。外展工作将侧重于中学科学教育，与来自当地两个学区的高中科学教师建立合作伙伴关系，为大量处于不利地位、社会经济地位较低的学生提供服务。为了弥合目前材料科学的进步和中学科学内容之间的差距，PI将建立“当地教育工作者网络”(LEN)计划，这将有助于改变目前高中的教育学实践。这一努力将建立在加州理工大学、加州州立大学洛杉矶分校(CSULA)以及洛杉矶联合学院(洛杉矶联合学院)和帕萨迪纳联合学院(帕萨迪纳联合学院)之间已经建立的成功关系的基础上。LEN计划的重点将是向高中教师参与者展示材料科学的最新进展，并帮助他们开发随后在课堂上教授给学生的教育模块。此外，PI将开发一门新的材料科学课程，重点放在纳米级材料的机械性能上，其中将纳入从这项研究中获得的知识。加州理工学院的研究生和本科生将被要求为材料科学的最新进展准备基于文献的科学报告，重点是机械性能，并将其提交给LEN计划的高中教师。

TECHNICAL: The device functionality directly depends on structural integrity and mechanical stability, driving the necessity to understand and to predict mechanical properties of materials at reduced dimensions. Yield and fracture strengths have been found to deviate from classical mechanics laws and therefore can no longer be inferred from the bulk response or from the literature. Unfortunately, the few existing experimental techniques for assessing mechanical properties at that scale are insufficient, not easily accessible, and are generally limited to thin films. In order to design reliable devices, a fundamental understanding of nano-scale mechanical response is desperately needed; with the remaining questions of whether materials really are stronger when the instrumental artifacts are removed and if so, then why and how. This project investigates fundamental plasticity mechanisms and defect evolution (specifically, dislocations) operating in nano-scale crystals subjected to a specified mechanical deformation. Experimentally determined stress-strain relationships will be enhanced by in-situ SEM observations, and microstructural characterization, which will help develop a comprehensive physical defect model consistent with the microscopic flow stress response. The project presents, for the first time a unified plan combining unique nano-scale sample preparation techniques with novel in-situ mechanical testing capability and post-deformation TEM microscopy. This project will take advantage of the PI's expertise in using Focused Ion Beam (FIB) as a unique tool for both nano-scale sample fabrication and subsequent manipulation and TEM cross-section preparation. Merging the boundaries across scientific disciplines will be essential in this project because to adequately address plasticity at the nano-scale, materials science, microscopy, and mechanics communities must combine their efforts. The research will cross length scales as it strives to identify and characterize dislocation processes occurring during deformation of crystalline materials whose dimensions are constrained to nanometer sizes. NON-TECHNICAL: With many nano-scale devices profoundly impacting our daily lives, this project lends itself as a perfect opportunity to make a broader impact. The outreach effort will focus on secondary science education by forming a collaborative with high school science teachers from two local school districts, serving large numbers of disadvantaged, low socio-economic, students. To bridge the gap between current progress in materials science and secondary science content, the PI will establish the "Local Educators Network" (LEN) program, which will help transform the current pedagogy practices in high schools. This effort will build upon the successful relationships already fostered between Caltech, Cal State University Los Angeles (CSULA), and the Los Angeles Unified (LAUSD) and Pasadena Unified (PUSD) School. The emphasis of LEN program will be to present updates on the latest progress in materials science to high school teacher participants and to help them develop educational modules to be subsequently taught to the students in their classrooms. In addition, the PI will develop a new course in materials science curriculum focusing on mechanical properties of materials at the nanoscale, which will incorporate the learning gained from this research. Caltech graduate and undergraduate students enrolled in this class will be required to prepare literature-based scientific reports on current progress in materials science with emphasis on mechanical properties and to present them to the high school teachers in the LEN program.