Study of Spin-Dependent Charge Transfer through Self-Assembled Monolayers of DNA on Metal Surfaces

脱氧核糖核酸(DNA)分子是生命的遗传密码，最近被证明具有惊人的电荷流动过滤能力。电荷是由通过每个分子的电子携带的。电子还具有一种称为自旋的本征性质，可以以两种(通常)同样可能的状态之一存在：自旋向上或自旋向下。令人惊讶的是，DNA分子可以根据电子的自旋来过滤传输的电子，这对它们在新兴技术应用中的应用具有令人兴奋的意义，这些应用需要在新生的自旋电子学领域中产生和操纵自旋极化电流。然而，导致过滤效应的机制仍然难以捉摸，也存在争议。为了评估DNA分子作为下一代自旋电子器件组件的实用性，必须测试和确定理论上预测的影响组装在金属表面的DNA分子的电子自旋过滤能力的参数。这项拟议的研究将利用二十年来对操纵分子组装的研究和最近的进展来开发和了解自旋极化的电子源。这项研究将结合纳米科学、纳米技术、自旋电子学、生物电子学和生物磁学等领域。在实验测试及其结果方面的具体进展将通过加州大学洛杉矶分校、国家和全球合作广泛提供。对这些影响的更深入了解将导致跨学科的重要发现；这些发现将通过演示文稿、出版物和强大的合作网络广泛传播。外展活动将面向年轻、代表性不足的科学家和广大公众，通过吸引当地高中教师和学生以及总部设在南加州的全球娱乐业。最近对生物系统中普遍存在的手性分子的自旋选择现象的观察表明，利用抗磁性分子进行有机自旋电子学具有独特的和令人兴奋的潜力。特别是，通过吸附在金属表面的脱氧核糖核酸(DNA)自组装单分子膜，观察到了前所未有的自旋选择性电子传输。虽然实验证据表明，组装的、定向的、手性DNA分子在室温下具有过滤电子自旋的能力，但导致这种现象的机制仍存在争议。一个社区认为，这种现象可能是分子本身固有的，因为许多理论模型将观察到的效应归因于非传统的Rashba型分子自旋-轨道耦合。相比之下，主要的理论小组认为，衬底和界面在自旋-轨道耦合中起着主要作用。仔细的实验测试将解开相对贡献，并将建立一种优化自旋选择和过滤的方法。我们将通过电化学方法建立稳健的品质因数来表征依赖于自旋的电荷传输。分子性质和底物材料将被系统地调整，以检验理论上预测的对这一现象的贡献。具体地说，包括重金属物种和底物同一性在内的分子化学和电子结构的改变将直接探测分子和界面内的自旋轨道耦合。这项工作将同时发展对自旋选择性电子-分子相互作用的基础理解，并批判性地评估最终将DNA和/或其他手性分子组装作为下一代有机自旋电子器件(如自旋过滤器、自旋转移扭矩磁阻随机存取器件和自旋极化有机发光二极管)中极化电子源的可行性。

Deoxyribonucleic acid (DNA) molecules, the genetic code of life, have recently been shown to possess a surprising filtering capacity for the flow of electric charge. The charge is carried by electrons that are transmitted through each molecule. Electrons also possess an intrinsic property known as spin, and can exist in one of two (usually) equally probable states: spin up or spin down. Surprisingly, DNA molecules can filter transmitted electrons based on their spin, holding exciting implications for their use in emerging technological applications that require the generation and manipulation of spin-polarized electrical currents within the nascent field of spintronics. However, the mechanism responsible for the filtering effect remains elusive and controversial. In order to assess the practicality of DNA molecules as components in next generation spintronic devices, the parameters that have been theoretically predicted to influence electron spin-filtering capacity by DNA molecules assembled on metal surfaces must be tested and determined. The proposed research will leverage two decades worth of studies on manipulating molecular assemblies and recent advances to develop and to understand spin-polarized sources of electrons. This research will combine the fields of nanoscience, nanotechnology, spintronics, bioelectronics, and biomagnetics. Specific advances in terms of experimental tests and their results will be made widely available both through UCLA, national, and global collaborations. Deeper understanding of these effects will lead to important discoveries across disciplines; findings will be broadly disseminated via presentations, publications, and strong collaborative networks. Outreach activities will target young, underrepresented scientists and the public at large by engaging local high school teachers and students, as well as the global entertainment industry based in Southern California. Recent observations of spin-selective phenomena involving chiral molecules prevalent in biological systems demonstrate the unique and exciting potential to utilize diamagnetic molecules for organic spintronics. In particular, unprecedented spin-selective electron transmission has been observed through self-assembled monolayers of deoxyribonucleic acid (DNA) adsorbed on metal surfaces. While experimental evidence has established that assembled, oriented, chiral DNA molecules have the capacity to filter electron spins at room temperature, the mechanism responsible for this phenomenon remains controversial. One community suggests that the phenomenon may be intrinsic to the molecule itself as many theoretical models attribute the observed effects to unconventional Rashba-type molecular spin-orbit coupling. In contrast, leading theory groups argue that the substrates and interfaces play major roles in spin-orbit coupling. Careful experimental tests will deconvolute the relative contributions and will establish a means to optimize spin selection and filtering. Robust figures of merit will be established to characterize spin-dependent charge transport via electrochemical methods. Molecular properties and substrate materials will be tuned systematically to test the theoretically predicted contributions to this phenomenon. Specifically, the modification of molecular chemical and electronic structures including the inclusion of heavy metal species and substrate identity will directly probe spin orbit coupling within the molecule and interface. This work will simultaneously develop a foundational understanding of spin-selective electron-molecule interactions and critically evaluate the practicability of ultimately implementing DNA and/or other chiral molecular assemblies as sources of polarized electrons in next generation organic spin electronic devices such as spin filters, spin-transfer torque magnetoresistive random access memory devices and spin-polarized organic light emitting diodes.