Collaborative Research: Tuning Graphene Nanoribbon Properties with Non-hexagonal Rings

在化学系大分子、超分子和纳米化学（MSN）项目的支持下，加州大学伯克利分校的Michael F. Crommie教授和哥伦比亚大学的Colin Nuckolls教授正在开发制造和表征新分子结构的方法，这些新分子结构有可能实现更快、更小、更节能的电子设备。目前的高科技应用包括采用相对较大的半导体晶体，并将其嵌入杂质，以及费力地将其切割成非常小的形状，以控制它们对电信号的反应。相比之下，这个合作研究团队将开发合成方法，以创造具有自然促进电子流动的形状和大小的线和片的分子类似物，并使其能够用作电子设备中的功能组件。如果成功的话，这个项目产生的新分子材料最终可能会提供一种更便宜、更清洁、更容易批量生产的半导体替代品，也可能提供比目前更小、更高效的电子设备（如晶体管、二极管和太阳能电池）。在进行该项目的过程中，学生和博士后研究人员将获得使用尖端仪器技术合成和表征新型纳米材料的宝贵经验。计划开展针对K12学生、少数族裔和普通大众的几项推广活动。这些活动包括举办实验室开放日、纳米科学海报会议和纳米技术研讨会；制作TikTok视频，突出化学和物理的结合，这是拟议研究的基础；并参加了几个社区服务项目，如向卓越转移（TTE） REU，湾区科学家激励学生（BASIS）和夏季数学和科学荣誉学院（SMASH）。该项目的主要目标是探索新的基于石墨烯纳米带（GNR）的系统，其电子和磁性能可以通过在GNR主链中嵌入非六边形碳环来调节。化学合成和原子尺度表征将结合起来评估这种新技术在控制自下而上制造的GNRs电子特性方面的效用。化学合成将用于开发新的分子前体和聚合物，通过表面自组装和基质辅助沉积（MAD），使具有工程环形结构的gnr能够在清洁的金属基底上生长。将使用扫描隧道显微镜（STM）表征GNR的局部电子和磁性能，并将与理论预测进行比较。一些基本的问题将被解决，比如通过在分子前体构建块中插入简单的非六边形环结构来控制GNR自由基态的程度。GNR内相邻基态杂化和现场库仑斥力之间的竞争将被调谐，目的是控制GNR的磁序，这是以前从未实现过的。新GNR系统的其他基本性质将被评估，如能量间隙、波函数分布、电子跳变振幅和自旋-自旋相互作用强度。如果成功，这项工作将有助于为自下而上制造gnr作为新的纳米电子学平台的使用奠定基础。这可能是革命性的，因为gnr具有优异的电子性能，并且可以从分子起始材料中以高保真度和原子精度批量合成。原则上，这可以使量子器件密度比其他材料平台高得多，成本非常低，为量子器件应用开辟了新的可能性，这将有利于社会。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。

With support from the Macromolecular, Supramolecular, and Nanochemistry (MSN) Program of the Division of Chemistry, Professors Michael F. Crommie of the University of California at Berkeley and Colin Nuckolls of Columbia University are developing methods for the fabrication and characterization of new molecular structures that have the potential to enable faster, smaller, and more energy efficient electronic devices. Current high technology applications involve taking relatively large semiconductor crystals and embedding them with impurities as well as laboriously cutting them into very small shapes to control how they respond to electrical signals. In contrast, this collaborative research team will develop synthetic methods to create molecular analogs of wires and sheets having shapes and sizes that naturally facilitate the flow of electrons and enable their use as functional components in electronic devices. If successful, the new molecular materials that result from this project could eventually provide a cheaper, cleaner, and easier-to-mass-produce alternative to bulk semiconductors, and could also provide smaller and more efficient electrical devices (such as transistors, diodes, and solar cells) than is currently possible. During the course of conducting this project, students and postdoctoral researchers will gain valuable experience in the synthesis and characterization of new nanomaterials using cutting edge instrumental techniques. Several outreach activities targeting K12 students, underrepresented minorities, and the general public are planned. These include hosting laboratory open-house days, nanoscience poster sessions, and nanotechnology workshops; developing TikTok videos that highlight the blend of chemistry and physics that underpins the proposed research; and participating in several community-service programs, such as the Transfer to Excellence (TTE) REU, the Bay Area Scientists Inspiring Students (BASIS), and the Summer Math and Science Honors Academy (SMASH). The main goal of this project is to explore new graphene nanoribbon (GNR)-based systems whose electronic and magnetic properties can be tuned by embedding non-hexagonal carbon rings into the GNR backbone. Chemical synthesis and atomic-scale characterization will be combined to evaluate the utility of this new technique for controlling the electronic properties of bottom-up-fabricated GNRs. Chemical synthesis will be performed to develop new molecular precursors and polymers that enable the growth of GNRs with engineered ring structures on clean metal substrates via surface self-assembly and matrix-assisted-deposition (MAD). GNR local electronic and magnetic properties will be characterized using scanning tunneling microscopy (STM) and will be compared to theoretical predictions. Fundamental questions will be addressed such as the degree to which GNR radical states can be controlled by inserting simple non-hexagonal ring structures into molecular precursor building blocks. Competition between hybridization of adjacent radical states and on-site Coulomb repulsion within GNRs will be tuned with the aim of controlling GNR magnetic order, something never before accomplished. Other fundamental properties of new GNR systems will be evaluated, such as energy gaps, wavefunction distributions, electron hopping amplitudes, and spin-spin interaction strengths. If successful, this work could help build a foundation for the use of bottom-up fabricated GNRs as a new nanoelectronics platform. This could be transformative since GNRs have excellent electronic properties and can be synthesized in bulk quantities with high-fidelity and atomic precision from molecular starting materials. This could, in principle, allow quantum device densities much higher than other material platforms at very low cost, opening new possibilities for quantum device applications that would be beneficial to society.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.