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缩小尺寸时的机械性能。屈服强度和断裂强度已被发现偏离经典力学定律，因此不能再从体响应或文献中推断出来。不幸的是，现有的几种实验技术在这种尺度上评估机械性能是不够的，不容易获得，而且通常仅限于薄膜。为了设计可靠的器件，迫切需要对纳米尺度的机械响应有一个基本的了解；剩下的问题是，当仪器人工制品被移除时，材料是否真的更坚固，如果是这样，那么原因和方式。该项目研究了在特定机械变形的纳米级晶体中运行的基本塑性机制和缺陷演变（特别是位错）。实验确定的应力-应变关系将通过原位SEM观察和微观结构表征得到增强，这将有助于建立与微观流动应力响应一致的综合物理缺陷模型。该项目首次提出了将独特的纳米级样品制备技术与新颖的原位力学测试能力和变形后TEM显微镜相结合的统一方案。该项目将利用PI在使用聚焦离子束（FIB）方面的专业知识，作为纳米级样品制造和后续操作以及TEM横截面制备的独特工具。在这个项目中，跨越科学学科的界限将是至关重要的，因为要充分解决纳米尺度上的可塑性问题，材料科学、显微镜和力学团体必须结合他们的努力。该研究将跨越长度尺度，因为它努力识别和表征在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：随着许多纳米级设备深刻地影响着我们的日常生活，这个项目使自己成为一个产生更广泛影响的绝佳机会。该项目将与两个地方学区的高中科学教师合作，以中学科学教育为重点，为大量社会经济地位低下的弱势学生提供服务。为了弥合材料科学与中学科学内容之间的差距，PI将建立“地方教育者网络”（LEN）计划，这将有助于改变高中目前的教学实践。这一努力将建立在加州理工学院、加州州立大学洛杉矶分校（CSULA）、洛杉矶联合学校（LAUSD）和帕萨迪纳联合学校（PUSD）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介绍材料科学的最新进展，并帮助他们开发教育模块，随后在课堂上教授给学生。此外，PI将开发一门新的材料科学课程，重点是纳米尺度材料的机械性能，这将结合从这项研究中获得的知识。参加本课程的加州理工学院研究生和本科生将被要求准备以文献为基础的科学报告，介绍材料科学的最新进展，重点是机械性能，并将其提交给LEN项目的高中教师。

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.