Microscopic Electronic Heterogeneity Studied with Ultrafast 2D Microscopy

在化学系化学结构、动力学和机理(CSDM-A)计划的支持下，威斯康星大学麦迪逊分校的Martin Zanni教授正在开发一种空间分辨的二维白光显微镜，用于研究钙钛矿微晶和半导体碳纳米管的异质薄膜中的电荷和激子输运。其目的是测量和理解激子和电荷扩散对结构几何和电子耦合中微观非均质性的依赖关系。这些属性很重要，因为它们影响能量和电荷在材料中移动的时间尺度和长度尺度。Zanni教授和他的学生将设计和建造一个2D白光显微镜，其中泵浦光束的焦点可以相对于探头进行光栅扫描。相应的图像将给出空间地图，将电子的异质性与激子和电荷扩散的时间尺度和长度联系起来。他们的研究将为超快2D光谱创造一种新型的高光谱成像技术，并可能使人们更好地理解将电子结构、激子/电荷扩散与纳米和微米尺度的不均匀联系起来的基础科学。Zanni教授和他的学生将参与到当地一所小学的外展活动，以及建造和测试一种符合人体工程学和轮椅可访问的激光桌子的新设计。有机和无机薄膜和晶体的电子结构决定了激子和电荷扩散的时间尺度和长度。溶液加工材料所固有的是改变电子结构的微米和纳米尺度的异质性。Zanni研究小组使用一种由超高速2D白光光谱仪建造的新显微镜，发现了各种材料中单个微晶体电子结构中微观异质性的空间模式。在两种不同类型的单态裂变材料中，观察到了边缘附近的带隙、缺陷和整个块体材料的可观数量的变化。在2D钙钛矿中，观察到双激子结合能的微米空间变化。考虑到这些观察结果，顺理成章地认为，具有空间异质电子结构的晶体也应该具有空间相关的激子扩散。这一建议的目的是通过研究微晶和薄膜微区内微米长度尺度上的激子/电荷扩散与电子异质性之间的联系来验证这一假设。为了做到这一点，将建造一种新版本的2D白光显微镜，其中泵浦光束的焦点可以相对于探测器进行光栅扫描。使用这种新的显微镜，将测量单线态裂变和2D钙钛矿微晶体中的超快动力学，以及专门设计的半导体碳纳米管薄膜。这些图像将给出空间地图，将电子的异质性与激子和电荷扩散长度联系起来。通过建造一种新型的超快显微镜并追求这项提议的目标，Zanni团队旨在更好地理解激子和电荷扩散是如何由亚晶体和子域长度尺度上的电子结构的异质性决定的。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

With support from the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) program in the Division of Chemistry, Professor Martin Zanni of the University of Wisconsin-Madison is developing a spatially resolved two-dimensional white-light microscope to study charge and exciton transport in perovskite microcrystals and heterogeneous thin films of semiconducting carbon nanotubes. The goal is to measure and understand the dependence of exciton and charge diffusion on microscopic heterogeneities in structural geometries and electronic couplings. These properties are important because they impact the timescale and length scales over which energy and charge moves through the material. Professor Zanni and his students will design and construct a 2D White-Light microscope in which the focus of the pump beam can be raster scanned relative to the probe. The corresponding images will give spatial maps that correlate electronic heterogeneity to exciton and charge diffusion timescales and lengths. Their studies will create a new type of hyperspectral imaging technique for ultrafast 2D spectroscopy and could lead to a better understanding of the fundamental science that links electronic structure and exciton/charge diffusion to nano-and micro-scale heterogeneities. Professor Zanni and his students funded by this grant will be involved in outreach to a local elementary school as well as build and test a novel design for an ergonomic and wheelchair accessible laser table. The electronic structure of organic and inorganic films and crystals dictates the timescale and length of exciton and charge diffusion. Inherent to solution processed materials are micro- and nanoscale heterogeneities that alter electronic structure. Using a new microscope built from an ultrafast 2D white-light spectrometer, the Zanni research group discovered spatial patterns of microscopic heterogeneities in electronic structure within single microcrystals across a variety of materials. In two different types of singlet fission materials, changes were observed in bandgap near edges, defects, and in appreciable quantities throughout the bulk material. In 2D perovskites, micron spatial variations in the binding energy of biexcitons were observed. With these observations in mind, it stands to reason that a crystal that has spatially heterogeneous electronic structure should also have spatially dependent exciton diffusion. The purpose of this proposal is to test that hypothesis by studying the link between electronic heterogeneity and exciton/charge diffusion on the micron length scale within microcrystals and domains of thin films. To do so, a new version of the 2D White-Light microscope will be built in which the focus of the pump beam can be raster scanned relative to the probe. Using this new microscope, the ultrafast dynamics in singlet fission and 2D perovskite microcrystals will be measured as will purposely engineered thin films of semiconducting carbon nanotubes. The images will give spatial maps that correlate electronic heterogeneity to exciton and charge diffusion lengths. By building a new type of ultrafast microscope and pursuing the aims of this proposal, the Zanni team aims to build a better understanding of how exciton and charge diffusion is dictated by heterogeneity in electronic structure on sub-crystallin and sub-domain length scales.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.