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

Nathan S.加州理工学院的刘易斯得到化学系大分子、超分子和纳米化学（MSN）项目的支持，研究伴随着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，技术上重要的半导体表面反应性的变化。 其目的是获得基本的洞察行为的转变，从材料组成的个别债券的材料形成的扩展一维，二维，并最终三维键合。 该项目通过开发利用表面反应性的尺寸依赖性变化的新反应途径来促进科学进步。 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，以提供深入了解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会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参与了该项目。 此外，研究结果被纳入新生化学课程材料，整合到对高中的推广计划，如果汁和项目海豹动手科学模块，并传达给各级非专业观众，并通过多种媒体渠道。 在这个项目中，探索了由材料尺寸和维度变化引起的半导体电子结构变化所实现的新反应类别。 该项目的重点是确定：1）哪类反应受固体的潜在电子结构的影响，2）此类反应是否可用于系统地实现纳米颗粒之间的有益电子耦合，以及，3）此类反应是否可用于共价连接三维材料，例如块状晶体，同时还提供对结构上不同的材料的电子耦合的控制。 该项目的范围包括Si表面上的反应，Si表面的小分子模型和Si纳米晶体。 该项目还包括对二维材料的反应，如石墨烯，六方氮化硼和锚定到Si表面的过渡金属硫属化物。 该项目还在开发共价官能化二维材料（如石墨烯）的方法，以实现层与层之间和异质结堆叠之间的强大电子连接和强相互作用。 官能化的二维材料被连接到共价键合到Si表面的连接体上，并且使用层和连接体的顺序添加将更多的层添加到叠层中，直到行为接近Si上的本体材料的行为，如通过XPS和光学表征方法所确定的。 这项工作正在发展的二维材料的堆栈开始在相同的行为作为散装材料的点的理解。这个奖项反映了NSF的法定使命，并已被认为是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的支持。

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.