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教授由化学系的大分子、超分子和纳米化学(MSN)计划支持，研究从小分子到纳米晶体和二维材料，以及从纳米晶体和二维材料到块状晶体固体的转变过程中具有重要技术意义的半导体表面反应性的变化。其目的是从根本上洞察由单个键组成的材料到由扩展的一维、二维乃至最终三维键形成的材料的行为转变。该项目通过开发新的反应途径来促进科学进步，这些反应途径利用了表面反应性的大小依赖变化。选择硅表面、硅表面的小分子模型和硅纳米晶作为关键的例子，以提供从纳米尺度到宏观尺度的化学连续体的洞察。正在开发的新反应路径可能会使新一代太阳能电池、传感器和电子器件的新接口以及其他相关硅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材料，整合到面向高中的推广计划中，例如来自Juice的果汁和项目海豹突击队员动手科学模块，并通过多种媒体渠道向各级非专业受众传播。在这个项目中，探索了由于材料的大小和维度的变化而导致的半导体电子结构的变化所引起的新的反应类别。该项目的重点是确定：1)哪类反应受固体基本电子结构的影响，2)这种反应是否可以用来系统地实现纳米颗粒之间有益的电子耦合，以及3)这种反应是否可以用来将三维材料，如大块晶体，与二维材料共价连接，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上的反应，硅表面的小分子模型，以及硅纳米晶。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硅表面的过渡金属硫化物。该项目还在开发使石墨烯等二维材料共价功能化的方法，以实现层之间和异质结堆栈之间的强大电子连接和强烈相互作用。功能化的二维材料被连接到共价结合到硅表面的连接物上，并且使用层和连接物的顺序添加到堆栈中，更多的层被添加到堆栈中，直到通过XPS和光学表征方法确定的行为接近于硅上的体相材料。这项工作正在发展对堆叠的二维材料开始在与散装材料相同的情况下表现的点的理解。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.