Charge Localization and Transport at Interfaces

非技术描述：碳基(有机)电子产品重量轻，价格相对便宜，但更难在商业上实现。它们的电性能关键取决于不同材料之间的界面电荷的分布情况。然而，最常见的分析是通过整体来报告性能，而忽略了电气行为良好和不良的根本原因。该项目采用了一种测量技术，提供了关于分子在材料界面上如何排列以及共享电荷的分子数量的信息。该项目专注于工作良好的材料，然后引入降低其性能的缺陷，监测这些缺陷对导电性和电荷所在分子数量的影响。在这些研究方向的同时，研究小组还设计并领导为期三天的年度外联活动--草原上的大学--的化学活动。这个项目招收了来自中西部农村社区的60名学生(6-11年级)，并向他们中的许多人介绍了化学在农业、能源转换中的作用，在许多情况下，他们开始了在大学水平上学习科学的过程。技术描述：电荷在材料界面的局域化程度对其迁移率有很大的影响，但很少有方法应用于特定于界面的有机电子薄膜。在这些特定于表面的方法中，只有振动和频产生能够同时报告分子的有序性和取向以及电荷局域化的程度。本项目旨在直接测量分子堆积和电荷局域化对有机材料界面电荷传输效率的影响。该研究小组将振动和频产生光谱应用于由一系列perene diimide分子膜构建的场效应晶体管，并观察了随着分子结构的变化，界面结构、迁移率和局部化的变化。他们还在电荷施主和受主之间引入了介质材料的平面厚度梯度，以逐渐减少局域化的程度，同时进行相同的光谱分析。最后，在产生振动和频的同时，利用光致电荷转移来制备电荷离域状态。总体而言，该项目确定了电荷局部化在有机薄膜界面传输中的作用。

Nontechnical Description: Carbon-based (organic) electronics are light-weight and relatively inexpensive, but have been more difficult to realize commercially. Their electrical performance depends crucially on how spread out electrical charges become at the interfaces between different materials. However, the most common analyses report on properties through the bulk, overlooking the underlying reasons for both good and bad electrical behaviors. This project employs a measurement technique that delivers information about how molecules are arranged at material interfaces and the number of molecules over which electrical charges are shared. The project focuses on materials that work well and then introduces defects that diminish their performance, monitoring the effect of these defects on conductivity and the number of molecules on which charges reside. In parallel with these research directions, the research team designs and leads the chemistry activities at an annual three-day outreach event called University on the Prairie. This program hosts 60 students (grades 6-11) from rural communities in the Midwest and introduces many of them to the role of chemistry in agriculture, energy conversion, and in many cases, begins the process by which they envision themselves studying science at a college level. Technical Description: The extent of localization of electrical charges at material interfaces has an enormous influence on their mobility, yet there are few characterization methods applied to organic electronic films that are interface specific. Of these surface specific approaches, only vibrational sum frequency generation has the ability to simultaneously report the molecular ordering and orientation as well as the extent of charge localization. This project seeks to directly measure the influence of molecular packing and charge localization on the efficiency of charge transport at organic material interfaces. The research team applies vibrational sum frequency generation spectroscopy to field-effect transistors constructed with a family of perylene diimide molecular films and observes the changes in interfacial structure, mobility, and localization as the molecular structure is varied. They also introduce planar thickness gradients of dielectric materials between charge donor and acceptor layers to progressively decrease the extent of localization, while carrying out the same spectroscopic analysis. Finally, photoinduced charge transfer is used to prepare charge delocalized states while vibrational sum frequency generation is performed. Overall, the project identifies the role of charge localization in transport at organic thin film interfaces.