Impact of Radical Polymer Architecture on Spin Transport

计算机技术的进步已经彻底改变了世界运作、交流和做生意的方式；然而，由于杰出的技术突破和有远见的实现，目前的微电子范式正在达到其计算性能的上限。因此，必须发现、开发和成熟依赖于新材料开发的新操作范式，从而使这些关键技术继续发展。将这一想法推向现实的一个有希望的推动力是基于自旋的量子计算。在这种情况下，自旋是指电子的一种固有性质，它不同于通常用于传导电子的固有电荷（即电流），并且它是一种可以操纵的性质，这样就存在自旋输运（即自旋电流）。该项目在美国国家科学基金会材料研究部聚合物项目的支持下，开发了有望具有先进自旋输运特性的新型聚合物材料。除了提供性能可能优于当前技术水平的系统外，使用聚合物作为自旋传输材料为该技术机遇创造低成本解决方案提供了机会。因此，该项目的成功执行可能会导致下一代量子计算材料易于集成到设备基础设施中。此外，该项目的教育和推广部分为不同群体的科学家和工程师提供了独特的经验，旨在扩大科学和工程的参与。除了为来自不同经济背景的高中生和本科生提供暑期研究机会外，该项目的研究生研究员还参加了一个国内实习生交换计划，以提高他们的技术技能。此外，基于该计划中使用的特定类别的聚合物，提供了一种新的大规模开放在线课程（MOOC），以便以快速和易于消化的方式将结果传达给广泛的受众。在这些方面，该项目推动了基础科学的界限，从而为促进国家繁荣和国防的新技术和新教育计划提供了清晰的翻译。聚合物科学界为推进有机电子材料的多种最终用途应用做出了贡献。因此，在阐明与这些大分子的化学和物理相关的基本基础方面已经付出了很多努力；然而，应用这些相同的聚合物科学工具来操纵大分子材料中的自旋输运的能力并不在同一水平上。此外，鉴于该领域的历史以及这些材料在推进关键设备技术方面取得的巨大成功，社区中的大多数工作都集中在共轭聚合物上。另一方面，自由基聚合物（即在其悬垂基团上具有稳定开壳位的非共轭大分子）是一类新的自旋传输有机材料，与大多数自旋传输材料相比，有两个关键的不同之处。首先，这些聚合物导体的碳基性质导致它们具有弱自旋轨道耦合，较高的自旋弛豫时间和较长的自旋扩散长度（即50 nm），而这些材料特性对于增强自旋输运是必不可少的。此外，与大多数共轭聚合物相比，自由基聚合物提供了不同的自旋输运环境。也就是说，它们稳定的开壳垂坠位的固有性质保证了自旋输运通过顺磁介质发生，这可以增加自旋扩散长度。在这些方面，该项目由美国国家科学基金会材料研究部的聚合物项目支持，建立了与大分子结构、纳米结构环境、磁性环境和自由基聚合物自旋输运性质相关的基本结构-性能-性能关系。此外，该项目还推进了当地美国化学会（ACS）项目SEED计划，该计划为来自经济困难背景的高中生提供暑期研究机会。此外，它还提供了一种与美国领先的聚合物合成小组进行学生交换的方法，以便对化学工程研究生进行交叉培训。最后，该项目还包括开发一门描述自由基聚合物基础知识的MOOC，因为目前还没有这样的课程。因此，该项目有可能在基础科学和更广泛的影响方面取得进展，同时也支持教育和推广活动。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。

Non-Technical SummaryAdvances in computing have revolutionized the way the world operates, communicates, and does business; however, due to outstanding technological breakthroughs and visionary implementation, the current microelectronics paradigm is reaching its upper limit of computing performance. As such, new operational paradigms, which will rely on the development of novel materials, must be discovered, developed, and matured such that these critical technologies continue to evolve. One promising thrust in pushing this idea towards reality is that of spin-based quantum computing. In this context, spin refers to an inherent property of electrons that is distinct from the inherent charge that is often used to conduct electrons (i.e., an electric current), and it is a property that can be manipulated such that there is transport of spin (i.e., a spin current). This project, with support from the Polymers program in NSF’s Division of Materials Research, develops new polymer materials that are anticipated to have advanced spin transport properties. In addition to providing systems with performance that is potentially better than the current state of the art, using polymers as the spin-transport material opens the opportunity of creating low-cost solutions to this technology opportunity. Therefore, successful execution of the project could lead to next-generation quantum computing materials that are readily integrated into device infrastructures. Furthermore, the educational and outreach components of the project provide unique experiences to a diverse group of scientists and engineers with an aim of broadening participation in science and engineering. In addition to providing summer research opportunities to high school students from economically-diverse backgrounds and undergraduate students, graduate student researchers on this project participate in a domestic trainee exchange program to advance their technical skills. Additionally, a new massive open online course (MOOC) based on the specific class of polymers utilized in this program is offered such that the results are communicated to a broad audience in a rapid and digestible manner. In these ways, the project pushes the bounds of fundamental science such that it offers clear translation to new technologies and new educational programs that advance national prosperity and national defense.Technical SummaryThe polymer science community has contributed to advancing organic electronic materials for multiple end-use applications. As such, much effort has been placed in elucidating the fundamental underpinnings associated with the chemistry and physics of these macromolecules; however, the ability to apply these same polymer science tools to manipulate spin transport in macromolecular materials is not at the same level. Moreover, most of the work in the community has focused on conjugated polymers given the history of the field and the good deal of success these materials have had in advancing key device technologies. On the other hand, radical polymers (i.e., nonconjugated macromolecules with stable open-shell sites present at their pendant groups) are a new class of spin-transporting organic materials and differ in two key ways relative to most spin transport materials. First, the carbon-based nature of these polymer conductors causes them to possess weak spin-orbit couplings, higher spin relaxation times, and long spin diffusion lengths (i.e., 50 nm) relative to many of their inorganic counterparts, and these materials characteristics are essential for enhanced spin transport. Additionally, radical polymers offer a different spin transport environment compared to most of their conjugated polymer counterparts. That is, the inherent nature of their stable open-shell pendant sites ensures that spin transport occurs through a paramagnetic medium, which could enhance the spin diffusion length. To these points, this project, supported by the Polymers program in NSF’s Division of Materials Research, establishes the underlying structure-property-performance relationships associated with the macromolecular architecture, nanostructural environment, magnetic environment, and spin transport properties of radical polymers. Furthermore, this project advances the local American Chemical Society (ACS) Project SEED Program, which provides summer research opportunities to high school students from economically-disadvantaged backgrounds. Moreover, it provides for a means by which to have a student exchange with a leading polymer synthesis group in the United States such that cross-training of chemical engineering graduate students occurs. Finally, the project includes the development of a MOOC describing radical polymer fundamentals, because a course like this does not exist currently. Therefore, the project has the potential to make inroads in terms of fundamental scientific and broader impact while also supporting educational and outreach activities.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.