CAREER: Atomic Structure and Growth of Nano-Particles

这个职业建议的重点是纳米级原子聚集体的结构。这个问题很重要，因为在相变初期会形成萌芽团簇或颗粒，而团簇结构影响相变和微观组织演变。此外，金属颗粒是重要的工业催化剂，纳米颗粒是纳米技术的基石。本提案将基于涉及纳米级平行电子相干束的新型纳米区电子衍射（NED）技术，开发结构表征和原子分辨率成像的新方法。NED允许衍射模式记录从单个粒子三维结构的确定。这些结果将有助于理解纳米粒子的原子结构。将使用改进的分析特高压扫描透射电子显微镜开发现场能力。这种分析能力对研究双金属纳米颗粒的合金化和相分离具有重要意义。通过对比实验和分子动力学模拟，我们将对粒子结构有更深入的了解。该项目的目标是利用结构知识作为对生长的反馈，以改善纳米颗粒的性能。研究的材料包括银纳米粒子模型体系和银/铜共晶体系。后续的研究将集中在Ag/Fe和Fe/Pt的磁性合金，以及催化Pt/Ru的结构与性能之间的关系。这项研究将与几个层次的教育相结合。该项目将开发新的方法，利用纳米大小的平行电子相干束来确定原子排列。该技术是通用的，原则上适用于单个大分子。要开发的现场能力将通过材料微分析中心（CMM）向更广泛的社区提供。所获得的知识将被纳入纳米结构表征的教学，并通过研讨会和学校用于推广活动。该项目的一个重要方面是以基于网络的研究软件和教程的形式为那些寻求将纳米科学纳入自己课程的教育者创建研究和教育工具。在此开发的教材也将填补目前材料科学教育的空白，向学生介绍分子衍射的概念。研究生和本科生的研究人员将通过实践研讨会、会议和纳米科学特定项目的合作进行培训。

This career proposal focuses on the structure of nano-scale atomic aggregates. The problem is important because embryonic clusters or particles form at the early stage of phase transformations and the cluster structure affects the phase transformation and microstructure evolution. Furthermore, metal particles are important industrial catalyst and nanoparticles are the building blocks for nanotechnology. This proposal will develop new approaches to structure characterization and atomic resolution imaging based on the new nano-area electron diffraction (NED) technique involving a nanometer-sized coherent beam of parallel electrons. NED allows diffraction patterns to be recorded from individual particles for 3-D structure determination. The results will contribute to the understanding of atomic structure in nanoparticles. In-situ capabilities will be developed using a modified analytical UHV scanning transmission electron microscope. The analytical capability will be very useful for studying alloying and phase separation in bimetallic nanoparticles. Insight about particle structure will be obtained by comparing experiment with molecular dynamics simulations. A goal of the project is to use the structural knowledge as a feedback to growth to improve the properties of the nano-particles. Materials to be studied include the model system of Ag nanoparticles and the eutectic Ag/Cu system. Later study will focus on magnetic alloys of Ag/Fe and Fe/Pt, and catalytic Pt/Ru to correlate structure with properties.The research will be integrated with education at several levels. This project will develop novel methods that make use of a nanometer-sized coherent beam of parallel electrons to determine atomic arrangements. The technique is general, and in principle, applicable to individual macromolecules. The in-situ capabilities to be developed will be available through the Center for Microanalysis of Materials (CMM) to the broader community. Knowledge gained will be incorporated for teaching nanostructure characterization and used for outreach activities through workshops and schools. An important aspect of the project is the creation of research and education tools in the form of web-based research software and tutorials for educators who seek to incorporate nanoscience in their own curricula. The teaching materials to be developed here will also fill a gap in current materials science education by introducing students to the concept of molecular diffraction. Graduate and undergraduate researchers will be trained through hands-on workshops, conferences and collaboration on nanoscience specific projects.