Achieving Molecular Level Control Over the Chemical, Electrochemical, and Electrical Properties of Crystalline Si Surfaces

加州理工学院的Nathan S. Lewis教授得到了化学系大分子、超分子和纳米化学（MSN）项目的支持，研究技术上重要的半导体表面的反应性变化，这些变化伴随着从小分子到纳米晶体和二维材料的转变，以及从纳米晶体和二维材料到大块结晶固体的转变。目的是获得从单个键组成的材料到扩展的一，二，最终三维键形成的材料的行为转变的基本见解。该项目通过开发新的反应途径，利用表面反应活性的大小依赖性变化，促进了科学的进步。硅表面，硅表面的小分子模型和硅纳米晶体被选为一个关键的例子，以提供洞察从纳米尺度到宏观尺度的化学连续体。正在开发的新反应途径可能使新一代太阳能电池，传感器和电子设备的新接口以及其他相关Si器件结构的新方法成为可能。来自不同背景的研究生和本科生都参与了这个项目。此外，研究成果被纳入新生化学课程教材，整合到面向高中的推广项目中，如Juice from Juice和Project SEAL动手科学模块，并通过多种媒体向各级非专业受众进行交流。在这个项目中，探索了由于材料尺寸和维度的变化而导致的半导体电子结构变化所导致的新型反应。该项目的重点是确定：1)哪类反应受到固体底层电子结构的影响，2)这些反应是否可以用于系统地实现纳米颗粒之间有益的电子耦合，以及3)这些反应是否可以用于共价连接三维材料（如块状晶体）和二维材料，同时还提供对结构不同材料的电子耦合的控制。该项目的范围包括硅表面的反应，硅表面的小分子模型和硅纳米晶体。该项目还包括在二维材料上的反应，如石墨烯、六方氮化硼和固定在Si表面的过渡金属硫族化合物。该项目还开发了共价功能化二维材料（如石墨烯）的方法，以实现层之间和异质结堆叠之间强大的电子连接和强相互作用。功能化的二维材料被连接到共价连接到Si表面的连接剂上，并且通过层和连接剂的顺序添加，更多的层被添加到堆叠中，直到通过XPS和光学表征方法确定的行为接近Si上的大块材料。这项工作正在发展一种理解，即二维材料堆叠开始表现出与块状材料相同的行为。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Professor Nathan S. Lewis of California Institute of Technology is supported by the Macromolecular, Supramolecular, and Nanochemistry (MSN) Program of the Division of Chemistry to study the changes in the reactivity of technologically important semiconductor surfaces that accompany the transition from small molecules to nanocrystals and two-dimensional materials, as well as from nanocrystals and two-dimensional materials to bulk crystalline solids. The aim is to gain fundamental insight into the transition in behavior from materials comprised of individual bonds to materials formed by extended one-, two-, and ultimately three-dimensional bonding. The project promotes the progress of science by developing novel reaction pathways that exploit the size-dependent changes in surface reactivity. Si surfaces, small-molecule models of Si surfaces, and Si nanocrystals are selected as a critical example to provide insight into the chemical continuum from the nanoscale to the macroscale. The novel reaction pathways being developed may enable a new generation of solar cells, new interfaces for sensors and electronic devices and new approaches to other related Si device constructs. Graduate and undergraduate students from diverse backgrounds are involved in the project. In addition, the research results are incorporated into Freshmen chemistry course material, integrated in outreach program towards high schools, such as Juice from Juice and Project SEAL hands-on science modules, and communicated to non-professional audiences at all levels and through multiple media outlets. In this project, new classes of reactions that are enabled by changes in the electronic structure of semiconductors that result from changes in the size and dimensionality of the material are explored. The project is focused on determining: 1) which classes of reactions are influenced by the underlying electronic structure of the solid, 2) whether such reactions can be used to systematically achieve beneficial electronic coupling between nanoparticles, and, 3) whether such reactions can be used to covalently link three-dimensional materials, such as bulk crystals, to two-dimensional materials while also providing control over the electronic coupling of the structurally dissimilar materials. The scope of the project includes reactions on Si surfaces, small-molecule models of Si surfaces, and Si nanocrystals. The project also includes reactions on two-dimensional materials such as graphene, hexagonal boron nitride, and transition-metal chalcogenides anchored to Si surfaces. This project is also developing methods to covalently functionalize two-dimensional materials, such as graphene, to allow robust electronic connections and strong interactions between layers and in heterojunction stacks. Functionalized two-dimensional materials are being attached to linkers covalently bonded to the Si surface, and more layers are being added to the stack using sequential addition of layers and linkers until the behavior approximates that of the bulk material on Si, as determined by XPS and optical characterization methods. This work is developing an understanding of the point at which stacks of two-dimensional materials begin to behave in the same was as bulk materials.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.