Collaborative Research: Photoswitchable Interlayer Exciton Devices from 2D Hybrid Heterostructures

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Collaborative Research: Photoswitchable Interlayer Exciton Devices from 2D Hybrid HeterostructuresThis grant will support a collaborative research program between Purdue University and the University of St. Thomas, which focuses on investigating two dimensional (2D) materials. Atomically thin transition metal dichalcogenides such as MoS2 and WSe2 show unique physical properties which may not be observed from bulk crystals. These include strong photoluminescence due to the recombination of an electron-hole pair, called exciton in a quantum mechanical term. When two dissimilar 2D materials are brought together (for example, MoS2/WSe2), a new phenomenon emerges. This is called interlayer exciton originating from strong interactions between the heterolayers. While there is an excitement about the interlayer excitons given their potential impact in diverse applications, the relevant mechanisms are not fully understood. This research introduces novel strategies to modulate the formation and behavior of interlayer excitons, thereby gaining a fundamental understanding and developing practical devices. Functional organic layers will interface with 2D heterostructures, including photosensitive molecules that can change the optical and electronic properties upon external light irradiation. This project will combine advanced experimental measurements with modeling and computational capabilities to elucidate the fundamental interactions between 2D materials and organic layers, and related interlayer exciton properties. The research will also be complemented by an educational and outreach program to advance the public understanding of nanoscale science and engineering. The activities include (i) development of new course materials, (ii) research-based engineering education for undergraduate students, and (iii) development of a hands-on module for K-12 students that illustrates the principles of 2D materials.The central goal of the research is to demonstrate 2D heterostructured hybrid devices from transition metal dichalcogenides and photochromic molecules and study the related optoelectronic properties. A library of functional molecules will be examined such that their highest occupied molecular orbital and lowest unoccupied molecular orbital levels will be switched by external signals such as irradiating wavelengths. The photoswitchable behaviors will be exploited for modulating the interlayer excitons in heterobilayers and several distinct device configurations will be investigated. The hybrid heterostructures will be constructed and studied with optical spectroscopy and conductive atomic force microscopy at Purdue University. Ab initio calculations based on density functional theory will be performed at the University of St. Thomas to guide and verify the experiments. The project team will together develop a mechanistic understanding of the key parameters that govern the photoswitchable interlayer exciton devices and underpin the structure-property relationship towards general design principles. The fundamental knowledge from this work will lay the foundations for understanding architectured 2D materials and providing novel optoelectronic devices, thus resulting in transformative impacts.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.