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)计划的支持下，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，这些方法有可能实现更快、更小和更节能的电子设备。目前的高科技应用包括将相对较大的半导体晶体嵌入杂质，以及费力地将它们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，以创建具有自然促进电子流动并能够将其用作电子设备功能部件的形状和大小的电线和板材的分子模拟。如果成功，由该项目产生的新分子材料最终可能提供一种更便宜、更清洁、更容易大规模生产的大宗半导体替代品，还可能提供比目前可能的更小、更高效的电子设备(如晶体管、二极管和太阳能电池)。在进行这个项目的过程中，学生和博士后研究人员将在使用尖端仪器技术合成和表征新的纳米材料方面获得宝贵的经验。计划了几项针对K12学生、代表性不足的少数族裔和普通公众的外联活动。其中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；开发TikTok视频，突出支持拟议研究的化学和物理的混合；以及参与几个社区服务计划，如向卓越转移(TTE)REU、旧金山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，其电子和磁性可以通过在GNR主干中嵌入非六角形碳环来调节。将结合化学合成和原子尺度表征来评估这种控制自下而上制造的GNR电子性质的新技术的实用性。将进行化学合成，以开发新的分子前体和聚合物，使其能够通过表面自组装和基质辅助沉积(MAD)在清洁的金属衬底上生长具有工程环结构的GNR。将使用扫描隧道显微镜(STM)表征GNR的局域电子和磁性，并将其与理论预测进行比较。本课程将讨论一些基本问题，例如通过将简单的非六角环结构插入到分子前体构件中，GNR自由基态可以在多大程度上得到控制。相邻基态的杂化和GNR内的现场库仑排斥之间的竞争将被调整，目的是控制GNR的磁序，这是以前从未完成的事情。还将评估新GNR系统的其他基本性质，如能隙、波函数分布、电子跳跃幅度和自旋-自旋相互作用强度。如果成功，这项工作可能有助于为自下而上制造的GNR作为新的纳米电子平台的使用奠定基础。这可能是变革性的，因为GNRs具有优异的电子性质，可以从分子起始材料中以高保真和原子精度大量合成。原则上，这可以以非常低的成本允许量子设备密度远远高于其他材料平台，为量子设备应用打开新的可能性，这将对社会有益。这一奖项反映了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。

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.