IMR: Development of a TEM Testing Stage with Atomic Position Resolution for Student Training, Education, and Research

理想的、无缺陷的晶体固体的最终凝聚力长期以来一直是一个有趣的理论抽象：由于始终存在的缺陷，“真正的”材料永远不会显示出它们的理想强度。然而，纳米结构中的机械失效在性质和数量上都不同于块状材料的失效行为，因此提供了一个将“真实”与“理想”联系起来的巨大机会。纳米结构的合成、表征和建模方面的最新发展要求开发一种与高分辨率透射电子显微镜相结合的仪器，并将使对半导体和绝缘体纳米线以及单壁碳纳米管等的断裂的全面研究成为可能。提出了一种新型的亚埃量级TEMMEMS机械加载平台。该仪器的硬件由五部分组成：柔性传动机构、运动执行器、MEMS试件夹持器(试片)、透射电子显微镜夹持器和位置控制系统。该仪器将允许研究因其新颖的结构而具有基本意义的材料体系，以及因其电、热和机械性能而具有实际重要性的材料体系。我们建议(I)开发和制造这种新的仪器(Ii)开发稳健的方法将纳米线和纳米管配置到测试平台上(Iii)对纳米结构的力学进行初步的实验测量以验证系统性能，以及(Iv)与多尺度理论和建模方面的专家互动，这些专家结合了电子结构、分子力学和连续介质力学计算，他们对所提出的仪器和它可以执行的测量非常感兴趣。被提议的团队拥有必要的技能来设计、制造、测试和使用基于TEMMEMS的测试阶段，用于研究材料在机械载荷下的响应，以及具有零到几个原子尺度缺陷的纳米结构的断裂和疲劳。硅、锗、掺杂的硅和锗纳米线以及调制成分的纳米线，如条状和核壳结构、二氧化钛纳米线和单壁碳纳米管的广泛潜在应用，突显了对纳米线断裂和疲劳的基本了解的重要性。将产生一种新的仪器和重要的新方法，以解决缺陷、界面、化学环境、循环机械载荷(疲劳)、应变率和电流存在对纳米线断裂力学的影响。预计纳米线(直径比头发小100倍)将被用于许多重要应用，例如在纳米电子学中(作为逻辑、存储器和互连元件)，由于其高表面积体积比和对表面相互作用的特殊敏感性而作为化学传感元件，在纳米机电系统(NEMS；作为机械部件、机电部件、致动器、应变仪、流量传感器等)、在结构复合材料中的单晶纳米线的晶体完整性预计将赋予特殊的刚性、强度和韧性，并可能在能量转换设备(作为热电元件)。正是由于这些原因，了解单晶纳米线的详细机制及其失效行为至关重要。了解纳米线断裂(材料如何断裂)和疲劳(例如，反复加载的材料最终如何失效)将为它们随后在存在机械应力的各种应用中的使用提供重要的知识基础。这项工作将对将在美国进一步开发和销售的新型仪器产生重大影响。基于TEMMEMS的测试阶段(这是一个可以安装在透射式电子显微镜中的微型测试阶段，具有使其发挥作用的微电子机械系统组件)，以及对单个纳米线的机械响应的研究，将激发世界各地科学家和工程师的想象力，从而点燃国际上对纳米结构力学的努力。科学家、工程师和公众的这一同样的“想象力”将意味着，这里概述的工作将提供教科书般的例子，说明如何使用智能工程来开发能够在如此精细的控制水平上可控地使纳米结构变形的仪器，以及由这种方法引起的机械响应、断裂和疲劳的基础研究。这项仪器开发工作包括一个重要的教育推广计划，包括为研究生和博士后研究员提供的研究计划，为本科生(包括少数族裔)和高中教师提供的暑期研究培训，增加化学和工程课程的课程材料，以及与以西北大学为中心的NSF纳米科学与工程学习与教学中心合作，为7-12年级开发课程。还计划向感兴趣的公司进行重要的技术过渡的第二阶段，并因此继续跟进，以确保美国和世界各地的研究人员能够获得这种仪器，以迅速加快其使用速度。这将提高纳米线重要机械和机电性能数据库的创建速度，这也将加快它们在重要应用中的使用。

The ultimate cohesive strength of an ideal, defect-free crystalline solid has long been an interesting theoretical abstraction: 'real' materials never exhibit their ideal strengths due to ever-present defects. However, mechanical failure in nanostructures is qualitatively and quantitatively distinct from the failure behavior of bulk materials, thus providing a tremendous opportunity to connect the 'real' to the 'ideal'Recent developments in the synthesis, characterization, and modeling of nanostructures warrant the development of an instrument that will operate in conjunction with high-resolution transmission electron microscopy, and will enable a comprehensive study of fracture in, e.g., semiconductor and insulator nanowires, and single walled carbon nanotubes. A novel TEM MEMS-based mechanical loading stage with sub-Angstrom-level resolution is proposed. The hardware of the proposed instrument consists of five components: a compliant transmission mechanism, a motion actuator, a MEMS specimen holder (coupon), a TEM holder, and a position control system. This instrument will allow study of material systems that are of fundamental interest due to their novel structure, and of practical importance due to their electrical, thermal, and mechanical properties. We propose (i) to develop and fabricate this new instrumentation (ii) to develop robust methods for configuring nanowires and nanotubes onto testing platforms (iii) to perform preliminary experimental measurements of the mechanics of nanostructures to verify system performance, and (iv) to interact with experts in multiscale theory and modeling that combines electronic structure, molecular mechanics and continuum mechanics calculations, who have an intense interest in the proposed instrument and the measurements it can perform. The proposed team has the skills necessary to design, fabricate, test, and use the TEM MEMS-based testing stage, for the study of materials response under mechanical load, and of fracture and fatigue of nanostructures having zero to a few atomic-scale defects. The importance of a fundamental understanding of fracture and fatigue in nanowires is underscored by the broad range of potential applications envisioned for Si, Ge, doped Si and Ge nanowires, as well as nanowires of modulated composition such as 'striped' and core-shell structures, TiO2 nanowires, and single walled carbon nanotubes. A new instrument and important new methods will result, to address the influence of defects, interfaces, chemical environment, cyclic mechanical loading (fatigue), strain rate, and the presence of an electric current, on the fracture mechanics of nanowires. It is envisioned that nanowires (100 times smaller in diameter than a hair) will be used in a host of important applications, such as in nanoelectronics (as logic and memory and interconnect elements), as chemical sensing elements due to their high surface to volume ratio and exceptional sensitivity to surface interactions, in nanoelectromechanical systems (NEMS; as mechanical components, electromechanical components, actuators, strain gauges, flow sensors, others), in structural composites where the crystalline perfection of single crystal nanowires is expected to confer exceptional stiffness, strength, and toughness, and potentially in energy conversion devices (as thermoelectric elements). It is for these reasons, among others, that it is critically important to understand the detailed mechanics of single crystal nanowires and their failure behavior. An understanding of nanowire fracture (how a material breaks) and fatigue (how a material that is repeatedly loaded, for example, eventually will fail) will provide an important base of knowledge for their subsequent use in diverse applications where mechanical stress will be present.This work will have a strong impact on novel instrumentation, which will be further developed and sold in the United States. The TEM MEMS-based testing stage (this is a tiny testing stage that can fit into a transmission electron microscope and has microelectromechanical systems components that allow it to function), and studies of the mechanical response of individual nanowires, will capture the imagination of scientists and engineers around the World, so that an international effort on mechanics of nanostructures will be ignited. This same "capturing of the imagination" of scientists and engineers and the general public will mean that the work outlined here will provide textbook examples of the use of clever engineering to develop instruments that can controllably deform nanostructures at such fine levels of control, and of fundamental studies of mechanical response, fracture, and fatigue that result from such approaches. This instrument development effort includes a significant program in education outreach, including research programs for graduate students and postdoctoral fellows, summer research training for undergraduate (including minority) students and high school teachers, additions to course materials being offered both in chemistry and engineering courses, and curriculum development for grades 7-12 in coordination with the NSF Center for Learning and Teaching in Nanoscale Science and Engineering centered at Northwestern University. There is also a plan for the important second phase of technology transition to interested companies, and thus of follow through to ensure that such instrumentation will be available to researchers in the USA and around the World, for rapid acceleration of their use. This will increase the rate of creation of databases of important mechanical and electromechanical properties of nanowires, which will also accelerate their use in important applications.