Symmetry Making and Breaking in the Synthesis and Assembly of Stellated and Bimetallic Nanocrystals

大自然在花朵的美丽、蜂巢的精确和雪花的精致图案中都展示了对称。除了对称形式的吸引力，对称还可以赋予功能。例如，球蛛编织成螺旋状，以最大限度地提高其网的强度，蜜蜂建造紧密排列的六边形蜂巢，以最大限度地储存蜂蜜。结构和功能之间的这种相关性也体现在现代纳米材料设计中，改变纳米晶体的对称性或由纳米晶体构建的上层结构的内部顺序可以赋予新的功能。然而，直到最近，纳米材料的合成和组装还局限于简单的成分和结构。在这项研究中，首席研究员Sara Skrabalak正在开发新的合成方法，以制造具有多种金属和确定形状的金属纳米结构。这些纳米结构也被用作构建更大结构的积木，积木的对称性决定了更大的上层结构的形状。首席研究员和她的学生还研究了这些材料的组成和结构是如何赋予其功能的。特别是，为了实现化学传感应用的多功能平台，人们正在研究新的光-物质相互作用，这种相互作用是对称的函数。最终，该研究通过在多个学科之间建立联系，包括纳米/无机/固态化学，凝聚态物理，表面科学和材料科学，在该领域具有更广泛的影响。该项目还包括向非科学家介绍纳米概念的推广和教育工作。该项目还让本科生参与研究活动，强调他们与周围社区的联系。印第安纳大学的Skrabalak小组正在开发一种新的多金属纳米结构合成策略，即多种金属同时沉积在形状可控的纳米晶体上。纳米晶种子的对称性被转移到最终的纳米结构中。这项研究包括研究晶格失配和沉积动力学对双金属分布的影响。这项工作与一项研究相结合，研究如何在种子介导的共还原过程中沿着特定的晶体学方向减少对称性，以实现新的星状纳米晶体对称性，从而实现功能多样化。最后，Skrabalak团队正在使用星状金属纳米晶体来组装密密的低密度晶格，以将结晶能力扩展到新的结构类别。它们还描述了出现的集体光学特性。这三个目标与推广和教育工作相结合，本科生研究人员成为他们以前高中的科学大使，向学生介绍纳米概念，并为那些对科学、技术、工程和数学领域感兴趣的人提供榜样。研究的进展扩展了纳米晶体和超结构的类别，并确定了种子和构建块对称在金属纳米晶体合成和组装中的作用，从而在科学上产生更广泛的影响。

Nature demonstrates symmetry in the beauty of a flower, the precision of a honeycomb, and the elaborate patterns of snowflakes. Beyond the appeal of symmetric forms, symmetry can also impart function. For example, orb spiders weave in a spiral pattern to maximize the strength of their webs and bees construct honeycombs with close packed hexagons to maximize honey storage. This correlation between structure and function is also captured in modern nanomaterial design, where changing the symmetry of a nanocrystal or the internal order of a superstructure built from nanocrystals can give novel function. However, the synthesis and assembly of nanomaterials have been limited to simple compositions and structures until recently. In this research, the principal investigator, Sara Skrabalak, is developing new synthetic methods to make metal nanostructures with multiple metals and defined shapes. These nanostructures are also being used as building blocks to form larger structures, where the symmetries of the building blocks direct the shapes of the larger superstructures. The principal investigator and her students also study how the compositions and structures impart functionality. In particular, studies into the new light-matter interactions that arise as a function of symmetry are underway in an effort to achieve multi-functional platforms for chemical sensing applications. Ultimately, this research has broader impacts in the field by forging links between multiple disciplines, including nano/inorganic/solid-state chemistry, condensed matter physics, surface science, and material science. This project also incorporates outreach and educational efforts that introduce nanoscale concepts to non-scientists. The project also involves undergraduates in research activities in ways that emphasize their connection to the surrounding community.The Skrabalak group at Indiana University is developing seed-mediated co-reduction as a new synthetic strategy to multimetallic nanostructures, where multiple metals are simultaneously deposited onto shape-controlled nanocrystals. The symmetry of the nanocrystal seeds is transferred to the final nanostructures. This research includes studying how lattice mismatch and deposition kinetics contribute to bimetallic distribution. This work is coupled with a study of how symmetry can be reduced along specific crystallographic directions during seed-mediated co-reduction in order to achieve new stellated nanocrystal symmetries and in turn functional diversification. Finally, the Skrabalak group is using the stellated metal nanocrystals to assemble close-packed and low-density lattices to expand crystallization capabilities to new structural classes. They also characterize the collective optical properties that emerge. These three aims are coupled with outreach and educational efforts in which undergraduate researchers are Science Ambassadors to their former high schools, introducing nanoscale concepts to students and serving as role models to those interested in science, technology, engineering and mathematics fields. Advancement in the research expands the classes of nanocrystals and superstructures possible and identifies the roles of seed and building block symmetry in the synthesis and assembly of metal nanocrystals for broader impact in the science.