Charge Localization and Transport at Interfaces

非技术描述：碳基（有机）电子产品重量轻，相对便宜，但在商业上实现起来比较困难。它们的电学性能主要取决于不同材料之间的界面上电荷的分布情况。然而，最常见的分析报告了整体的特性，忽略了良好和不良电气行为的潜在原因。该项目采用了一种测量技术，可以提供有关分子如何在材料界面上排列以及电荷共享的分子数量的信息。该项目将重点放在性能良好的材料上，然后引入降低其性能的缺陷，监测这些缺陷对电导率和带电分子数量的影响。在这些研究方向的同时，研究小组设计并领导了为期三天的年度推广活动“草原上的大学”的化学活动。该项目接待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、能量转换中的作用，在许多情况下，他们开始设想自己在大学水平上学习科学。技术描述：材料界面上电荷的定位程度对其迁移率有巨大的影响，但很少有表征方法应用于界面特定的有机电子薄膜。在这些表面特异性方法中，只有振动和频率生成能够同时报告分子的有序和取向以及电荷的局部化程度。本项目旨在直接测量分子包装和电荷定位对有机材料界面电荷输运效率的影响。研究小组将振动和频率产生光谱应用于由苝二亚胺分子膜构成的场效应晶体管，观察了分子结构变化时界面结构、迁移率和局域化的变化。他们还在电荷供体层和受体层之间引入介电材料的平面厚度梯度，以逐步降低局部化程度，同时进行相同的光谱分析。最后，利用光诱导电荷转移制备电荷离域态，同时进行振动和频率的产生。总体而言，该项目确定了电荷定位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.