Collaborative Research: Charge Transport in Helicoidal Molecular Crystals

非技术抽象晶体是直的定义。它们有锋利的边缘和平坦的表面。它们是多面体。然而，分子晶体在生长时会扭曲，这是非常常见的，尽管鲜为人知。超过三分之一的简单分子晶体能够形成扭曲形态。作为一种基本上未被探索的现象，晶体扭曲为材料设计引入了一个新的维度。塑料电子设备，例如可折叠LCD屏幕，智能手机，计算机和太阳能电池板，取决于携带电力的微小晶体的形状。该合作项目由NSF材料研究部门的固态和材料化学计划支持，在基础科学层面揭示了扭曲形态对电流和光通过有机半导体晶体传播的影响，以迎接下一个时代的个人消费电子设备以及与可再生能源相关的关键技术。早期的研究结果表明，扭转可以提高导电性。涵盖文学，艺术，历史和教育的外展活动反映了晶体和手性的主题（可以从镜像中区分出来的物品是手性的，例如手），这些科学工作的基础，重点是使用扭曲晶体的有趣方面作为一个平台，让K-12学生参与纽约都会区的STEM相关活动。技术摘要螺旋晶体的间距为1-500微米，当从形成传统有机半导体的分子中生长出来时，它可以携带电荷。在器件层面，这些长度尺度上的扭曲可能对光传播和电荷注入、提取和跳跃产生关键影响。为了阐明扭曲对这些过程的一般影响，一系列半导体化合物被诱导扭曲，因为它们从熔体中结晶成薄膜，作为这项合作研究的一部分，这是由NSF材料研究部的固态和材料化学计划支持的。导电和光电导原子力显微镜和电荷迁移率测量使用场效应晶体管平台上进行这些螺旋晶体作为间距的函数，以确定调制的电场和光诱导的电荷传输局部沿着和垂直于扭转轴。由于光电器件通常需要在有源层内的特定晶体取向以获得最佳性能，因此将电结晶应用于熔融有机导体以准直电极表面上的扭曲晶体。电磁手征各向异性测量，结合完整的成像旋光独特的PI的实验室，实现了通过扭曲引入的手性缺陷的搜索。在这样做的过程中，这项研究揭示了晶体生长的基本机制，同时解决了有机电子领域的固有局限性，包括沿着沿着较难接近的晶体方向的大的电荷传输各向异性和独立于分子结构的调节分子相互作用的困难。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的评估来支持。影响审查标准。

Non-technical abstract Crystals are straight by definition. They have sharp edges and flat faces. They are polyhedra. However, molecular crystals that twist as they grow are remarkably common, albeit little known. More than one third of simple molecular crystals are capable of forming twisted morphologies. As a largely unexplored phenomenon, crystal twisting introduces a new dimension to materials design. Plastic electronic devices, e.g. foldable LCD screens, smart phones, computers, and solar panels, depend on the shapes of tiny crystals that carry electricity. This collaborative project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research at NSF, uncovers at a fundamental science level the effect of twisted morphologies on the propagation of electrical current and light through crystals comprising organic semiconductors in order to usher in the next age of personal consumer electronic devices as well as critical technologies associated with renewable energy. Early results show that twisting boosts conductivity. Outreach activities embracing literature, art, history, and education reflect the themes of crystals and chirality (items that can be distinguished from their mirror image are chiral, for example a hand) that undergird these scientific efforts, with a focus on using intriguing aspects of twisted crystals as a platform to engage K-12 students in STEM-related activities in the NY metro area. Technical AbstractHelicoidal crystals with pitches from 1-500 microns can carry charge when grown from molecules that form traditional organic semiconductors. At the level of devices, twisting on these length scales can have critical consequences on light propagation and charge injection, extraction and hopping. To elucidate the general effect of twisting on such processes, a series of semiconducting compounds are induced to twist as they crystallize from the melt into thin films as part of this collaborative research, which is supported by the Solid State and Materials Chemistry program in the Division of Materials Research at NSF. Conductive and photoconductive atomic force microscopy and charge mobility measurements using a field-effect transistor platform are performed on these helicoidal crystals as a function of pitch to determine the modulation of electric field- and photo-induced charge transport locally along and perpendicular to the twisting axes. As optoelectronic devices typically require specific crystal orientations within active layers for optimal performance, electrocrystallization is applied to molten organic conductors to collimate twisted crystals on electrode surfaces. Electrical magnetochiral anisotropy measurements, in conjunction with complete imaging polarimetry unique to the PIs' laboratories, are actualized in the search for chiral defects introduced via twisting. In doing so, this research uncovers fundamental mechanisms of crystal growth while addressing inherent limitations in the field of organic electronics, including large charge transport anisotropies along less accessible crystallographic directions and difficulties in tuning molecular interactions independent of molecular structure.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.