In situ TEM mechanical molding of intermetallic nanowires

具有受控形状和高样品质量的纳米结构的大规模制造对于许多应用来说将是变革性的，例如传感、催化、等离子体和电子应用，但仍然具有挑战性。 最近，热机械成型，其中散装原料被压到模具上的纳米尺寸的孔，已经显示出制造大阵列的单晶纳米线的能力，具有良好控制的直径和长度，因此具有广泛的影响，上面列出的许多应用。 然而，这些纳米线是如何在热机械成型过程中形成的还没有很好的理解，严重限制了这种技术的广泛适用性。该项目旨在通过使用原位透射电子显微镜（TEM）直接实时观察热机械成型过程中金属系统纳米线的形成，从根本上了解原子尺度上的成型过程。 这些新知识将有助于通过在加工过程中提供基础科学来改进热机械成型技术，以便更好地选择控制这些制造的纳米线的尺寸和纵横比所需的加工条件，并且适用于可以热机械成型的更广泛类别的材料，并且允许更容易地生产大量的纳米级材料。 此外，该项目将为本科生提供研究机会，进行纳米金属系统的研究，从而为他们在先进的纳米制造业的就业机会做好准备。 原位TEM电影将与K-12学生和公众分享，以教育和参与公众在纳米科学和manufacturing.Technical SummaryNanoscale热机械成型，其中散装原料被压到模具上的纳米级通道在熔融温度的一小部分，最近已经证明了生产有序相的单晶纳米线的大阵列的能力。该项目旨在通过使用透射电子显微镜（TEM）的原子尺度结构表征来了解热机械成型的扩散过程，包括非原位和原位，以及各种金属间化合物和固溶体系统。重结晶的过程中，单晶纳米线从多晶散装原料中挤出的机制，将详细研究，以解释扩散动力学，严格控制的吉布斯自由能的降低，这取决于相当敏感的金属间化合物或固溶体的化学计量。原位TEM提供了扩散机制的实时信息，也可以证明排除常见的位错滑移和晶界运动。 总之，该项目将提供关于金属间化合物和固溶体的纳米级固体扩散过程的原子尺度信息，这是目前在很大程度上未探索的。 这种直接可视化的固体扩散在有限的渠道也将有助于建立一个更好地了解蠕变行为在纳米尺度。这些新知识将有助于开发热机械成型作为一种更简单和定制的纳米材料生产方法，用于广泛的技术应用。对于推广，在该项目下获得的原位TEM电影将被用作视觉工具，教育K-12学生和公众关于原子运动的基本方面及其与纳米制造的相关性。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

Non-technical SummaryLarge-scale manufacturing of nanostructures with controlled shapes and high sample quality will be transformative for many applications, such as sensing, catalysis, plasmonic and electronic applications, yet still challenging to achieve. Recently, thermomechanical molding, in which bulk feedstocks are pressed onto a mold with nano-sized pores, has shown the ability to fabricate large arrays of single-crystalline nanowires with well-controlled diameters and lengths, thus having broad implications for the many applications listed above. However, how these nanowires are formed during thermomechanical molding is not well understood, severely limiting the broad applicability of this technique. This project aims to fundamentally understand the molding process at the atomic scale by the use of in situ transmission electron microscopy (TEM) to directly observe in real-time the formation of nanowires of metallic systems during thermomechanical molding. Such new knowledge will help to improve the thermomechanical molding technique by providing the underlying science during processing in order to better select the processing conditions needed to control the dimensions and aspect ratios of these manufactured nanowires and be applicable to a broader class of materials that can be thermomechanically molded, and allow for more facile production of large quantities of nanoscale materials. Additionally, the project will provide research opportunities to undergraduate students to perform research in nanoscale metallic systems, thus preparing them for career opportunities in advanced nanomanufacturing. The in situ TEM movies will be shared with K-12 students and the general public in order to educate and engage the public in nano- science and manufacturing.Technical SummaryNanoscale thermomechanical molding, in which bulk feedstocks are pressed onto a mold with nanoscale channels at a fraction of the melting temperature, has recently demonstrated the capability to produce large arrays of single-crystalline nanowires of ordered phases. This project aims to understand the diffusion process of the thermomechanical molding by atomic scale structure characterization using transmission electron microscopy (TEM), both ex situ and in situ, with various intermetallic and solid-solution systems. The process of recrystallization, the mechanism in which a single-crystalline nanowire is extruded out from a polycrystalline bulk feedstock, will be examined in detail to explain diffusion dynamics that are tightly regulated by lowering of the Gibbs free energy, which depends quite sensitively to the stoichiometry of the intermetallics or solid solution. In situ TEM provides real-time information on the diffusion mechanism that could also demonstrate the exclusion of common dislocation slips and grain boundary movements. In summary, the project will provide atomic scale information on nanoscale solid diffusion processes of intermetallics and solid solutions, which is currently largely unexplored. Such direct visualization of solid diffusion in confined channels will also help to establish a better understanding of creep behaviors at the nanoscale. This new knowledge will help develop thermomechanically molding as a more facile and tailored production method of nanoscale materials for a broad range of technical applications. For outreach, the in situ TEM movies obtained under the project will be used as visual tools to educate K-12 students and general public about the fundamental aspects of atomic motions and their relevance to nanomanufacturing.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.