Controlling exciton dynamics at interfaces using moiré potentials

非技术概述：二维（2D）层状晶体，如过渡金属二硫属化物，最近受到了广泛关注。值得注意的是，它们的特性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。控制材料特性的一种有希望的方法是改变两个原子级薄晶体的相对取向和晶格尺寸，以创建纳米级莫尔图案。该项目将联合收割机二维层状晶体与分子晶体相结合，以产生广泛的莫尔图案。然后，研究小组将研究光学和电子特性对不同类型莫尔图案的依赖性。该项目获得的基础知识使研究人员能够创建可用于太阳能电池，LED和光电探测器以及量子发射器等设备的定制接口。该项目将在合作环境中培养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。对公众的推广活动包括为K-12学生举办夏令营、推广研讨会和科学推广网站。技术概要：通过弱的货车德瓦尔斯力，将2 D过渡金属二硫属化物晶体与有机分子晶体接合，可以产生广泛的莫尔图案。莫尔图案产生纳米尺度的周期性电势，这反过来又提供了一种独特的方式来控制界面处的电子动力学。研究小组结合了理论和实验的努力，以了解莫尔势如何影响界面处形成的层间激子（IX）的性质。目标是寻找具有两种不同类别的莫尔电位的界面，这两种莫尔电位有利于光电转换或发光，并证明莫尔电位是控制自由载流子产生和IX的辐射复合之间竞争的有效方法。时间分辨和/或角度分辨的光电子能谱，和时空光学泵浦探测光谱的组合被用来探测IX动态和带结构的接口。实验测得的IX动力学与能带排列，界面相互作用，和摩尔势确定的理论方法的基础上密度泛函理论，包括元-GGA的快速筛选和混合泛函更准确的计算。明确包括货车范德华相互作用。Wannier函数用于模拟莫尔条纹电位。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值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.