Controlling exciton dynamics at interfaces using moiré potentials

非技术综述：二维层状晶体，如过渡金属二卤化物，最近受到了极大的关注。值得注意的是，它们的性质可以通过将不同的晶体堆叠在一起来定制，而不需要传统无机半导体中的晶格匹配。控制材料性能的一种有希望的方法是改变两个原子薄晶体的相对取向和晶格尺寸，以产生纳米级的莫尔图案。该项目将2D层状晶体与分子晶体相结合，以产生广泛的莫尔图案。然后，研究小组将研究不同类型的莫尔图案对光学和电学特性的依赖。通过这个项目获得的基础知识使研究人员能够创造出在太阳能电池、LED、光电探测器以及量子发射器等设备中有用的定制接口。该项目将在协作环境中培训本科生和研究生在纳米材料设计、制造和表征方面的尖端研究能力。将特别强调从代表性不足的群体中招收学生。面向公众的外展活动包括为K-12学生举办的夏令营、外展研讨会和科学外展网站。技术摘要：通过弱范德华力将2D过渡金属二卤化物晶体与有机分子晶体对接，可以创建广泛的莫尔图案。莫尔图案产生了纳米级的周期性电势，这反过来又提供了一种独特的方式来控制界面上的电子动力学。研究小组将理论和实验相结合，以了解莫尔势如何影响在界面形成的层间激子(IX)的性质。我们的目标是寻找具有两种不同莫尔势的界面，这些界面有利于光电转换或光发射，并证明莫尔势是控制自由载流子生成和IX辐射复合之间竞争的有效方法。用时间分辨和/或角度分辨光电子能谱和时空光抽运探测光谱相结合的方法来探测界面上的Ix动力学和能带结构。实验测量的IX动力学与能带排列、界面相互作用以及基于密度泛函理论的理论方法确定的莫尔势相关联，这些理论方法包括用于快速筛选的Meta-ggas和用于更精确计算的混合泛函。范德华相互作用被明确包括在内。Wannier函数被用来模拟莫尔势。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。

NON-TECHNICAL SUMMARY:Two-dimensional (2D) layered crystals, such as transition metal dichalcogenides, have received much attention recently. Notably, their properties can be tailored by stacking different crystals together without the requirement of lattice matching found in traditional inorganic semiconductors. One promising way to control material properties is to vary the relative orientation and the lattice size of the two atomically thin crystals to create a nanoscale moiré pattern. This project will combine 2D-layered crystals with molecular crystals to produce a wide range of moiré patterns. The research team will then investigate the dependence of optical and electronic properties on the different types of moiré patterns. The fundamental knowledge gained by this project allows researchers to create tailor-made interfaces useful in devices such as solar cells, LEDs, and photodetectors, as well as quantum emitters. The project will train undergraduate and graduate students on cutting-edge research capabilities in nanoscale material design, fabrication, and characterization in a collaborative environment. There will be a particular emphasis on recruiting students from underrepresented groups. Outreach activities to the public include a summer camp for K-12 students, outreach seminars, and science outreach websites.TECHNICAL SUMMARY:A wide range of moiré patterns can be created by interfacing 2D transition metal dichalcogenide crystals with organic molecular crystals through weak van der Waals forces. The moiré pattern produces a nanoscale-periodic potential, which in turn provides a unique way to control the electron dynamics at the interface. The research team combines theoretical and experimental efforts to understand how the moiré potential affects the properties of the interlayer exciton (IX) formed at the interface. The goal is to search for interfaces with two distinct classes of moiré potential that favor either photo-to-electrical conversion or light emission, and to demonstrate the moiré potential as an effective way to control the competition between the free carrier generation and the radiative recombination of the IX. A combination of time-resolved and/or angle-resolved photoemission spectroscopy, and spatiotemporal optical pump-probe spectroscopy are used to probe the IX dynamics and the band structure at the interface. The experimentally measured IX dynamics are correlated with band alignments, interface interactions, and the moiré potential determined by theoretical methods based on density functional theory, including meta-GGAs for rapid screening and hybrid functionals for more accurate calculations. van der Waals interactions are explicitly included. Wannier functions are used to simulate moiré potentials.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.