Ultrafast spectroscopy beyond the diffraction limit: elucidating charge and lattice interactions with individual grain boundaries

对材料中的电和热运输过程的基本了解和有效设计非常重要，因为我们的能源基础设施的效率以及电子设备、运输和电力系统的可靠性能都受到这些过程的显著影响。由晶界分隔的微米级晶体组成的多晶材料是一类重要的材料，广泛应用于薄膜太阳能电池、高性能热电组件、电子和光子器件等领域。电能和热能如何通过晶界转移对多晶材料的宏观输运性质和器件性能有很大的影响。目前，对这些微观过程的详细了解仍然缺乏。该项目的首要目标是开发理论和实验技术，以阐明跨越单个晶界的局部能量传输过程。具体地说，研究小组将使用超快光学和电子光谱仪来检查这些过程如何受到晶界的形态、结构和无序的影响。该项目支持通过实践课程项目和短期课程向K-12和本科生宣传可再生能源技术的教育活动。为了促进可再生能源劳动力的多样性，研究团队还为来自代表性不足的少数族裔社区的高中和本科生研究人员提供研究机会。深入了解具有复杂微观结构的功能材料的结构-性能关系是现代材料科学长期追求的目标。晶界是最常见的显微组织之一，对宏观性能有重要影响。尽管晶界在功能材料中的重要性至高无上，但以往的研究大多集中在宏观晶界集合和/或静态和平衡条件下的平均效应。该项目旨在通过将最先进的第一原理模拟与具有高时空分辨率的超快光学和电子光谱学相结合来应对这一挑战。具体地说，研究小组将研究多晶硅、多晶钙钛矿和纳米结构热电材料中的单个晶界，了解它们与电子和声子的局部相互作用以及它们对宏观电和热电传输特性的影响。这个项目提供了一个系统的了解如何个别晶界影响局域电子和声子输运性质，特别是在动态和非平衡条件下。这一知识可以提供变革性的机会，以“一次一粒”的自下而上的方法制造功能材料。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。

Fundamental understanding and effective engineering of electrical and thermal transport processes in materials is important, as the efficiency of our energy infrastructure and the reliable performance of electronic devices, the transportation and the power systems are significantly affected by these processes. Polycrystalline materials consisting of microscale crystal grains separated by grain boundaries are an important class of materials widely used in thin-film solar cells, high-performance thermoelectric modules and electronic and photonic devices. How electrical and thermal energy is transferred across the grain boundaries strongly impacts the macroscopic transport properties of polycrystalline materials and device performance. Currently, a detailed understanding of these microscopic processes is still lacking. The overarching goal of this project is to develop theoretical and experimental techniques to elucidate local energy transport processes across individual grain boundaries. Specifically, the research team will use ultrafast optical and electron spectroscopies to examine how these processes are affected by the morphology, structure and disorder of the grain boundaries. This project supports educational activities to advocate renewable energy technologies to K-12 and undergraduate students through hands-on class projects and short classes. To promote diversity in the renewable energy workforce, the research team also provides research opportunities to high school and undergraduate researchers from underrepresented minority communities. A thorough understanding of the structure-property relationship of functional materials with complex microstructures has been a longstanding goal for modern materials science. Grain boundaries are among the most common microstructures with significant influence on the macroscopic properties. Despite the paramount importance of grain boundaries in functional materials, most previous studies have focused on the average effect of a macroscopic ensemble of grain boundaries and/or under static and equilibrium conditions. This project aims to address this challenge by combining state-of-the-art first-principles simulations with ultrafast optical and electron spectroscopy with high spatial-temporal resolutions. Specifically, the research team will examine individual grain boundaries in multicrystalline silicon, polycrystalline perovskites and nanostructured thermoelectric materials regarding their local interactions with electrons and phonons and their impact on the macroscopic electrical and thermoelectric transport properties. This project provides a systematic understanding of how individual grain boundaries affect local electron and phonon transport properties, especially under dynamic and non-equilibrium conditions. This knowledge can enable transformative opportunities to build functional materials with a bottom-up approach, "one grain at a time".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.