title: Multimodal Nonlinear Optical Imaging of MoS₂ and MoS₂-Based van der Waals Heterostructures.
abstract: van der Waals layered structures, notably the transitional metal dichalcogenides (TMDs) and TMD-based heterostructures, have recently attracted immense interest due to their unique physical properties and potential applications in electronics, optoelectronics, and energy harvesting. Despite the recent progress, it is still a challenge to perform comprehensive characterizations of critical properties of these layered structures, including crystal structures, chemical dynamics, and interlayer coupling, using a single characterization platform. In this study, we successfully developed a multimodal nonlinear optical imaging method to characterize these critical properties of molybdenum disulfide (MoS2) and MoS2-based heterostructures. Our results demonstrate that MoS2 layers exhibit strong four-wave mixing (FWM), sum-frequency generation (SFG), and second-harmonic generation (SHG) nonlinear optical characteristics. We believe this is the first observation of FWM and SFG from TMD layers. All three kinds of optical nonlinearities are sensitive to layer numbers, crystal orientation, and interlayer coupling. The combined and simultaneous SHG/SFG-FWM imaging not only is capable of rapid evaluation of crystal quality and precise determination of odd-even layers but also provides in situ monitoring of the chemical dynamics of thermal oxidation in MoS2 and interlayer coupling in MoS2-graphene heterostructures. This method has the advantages of versatility, high fidelity, easy operation, and fast imaging, enabling comprehensive characterization of van der Waals layered structures for fundamental research and practical applications.
authors.affiliation: Department of Electrical and Computer Engineering, University of Nebraska-Lincoln , Lincoln, Nebraska 68588-0511, United States.
authors.forename: Dawei
authors.initials: D
authors.lastname: Li
authors.affiliation: Department of Electrical and Computer Engineering, University of Nebraska-Lincoln , Lincoln, Nebraska 68588-0511, United States.|Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology , 1037 Luoyu Road, Wuhan 430074, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Xiong
authors.affiliation: Department of Electrical and Computer Engineering, University of Nebraska-Lincoln , Lincoln, Nebraska 68588-0511, United States.
authors.forename: Lijia
authors.initials: L
authors.lastname: Jiang
authors.affiliation: Department of Physics and Astronomy, Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln , Lincoln, Nebraska 68588-0511, United States.
authors.forename: Zhiyong
authors.initials: Z
authors.lastname: Xiao
authors.affiliation: Department of Electrical and Computer Engineering, University of Nebraska-Lincoln , Lincoln, Nebraska 68588-0511, United States.
authors.forename: Hossein Rabiee
authors.initials: HR
authors.lastname: Golgir
authors.affiliation: Department of Electrical and Computer Engineering, University of Nebraska-Lincoln , Lincoln, Nebraska 68588-0511, United States.
authors.forename: Mengmeng
authors.initials: M
authors.lastname: Wang
authors.affiliation: Department of Electrical and Computer Engineering, University of Nebraska-Lincoln , Lincoln, Nebraska 68588-0511, United States.
authors.forename: Xi
authors.initials: X
authors.lastname: Huang
authors.affiliation: Department of Electrical and Computer Engineering, University of Nebraska-Lincoln , Lincoln, Nebraska 68588-0511, United States.
authors.forename: Yunshen
authors.initials: Y
authors.lastname: Zhou
authors.affiliation: Department of Electrical and Computer Engineering, University of Nebraska-Lincoln , Lincoln, Nebraska 68588-0511, United States.
authors.forename: Zhe
authors.initials: Z
authors.lastname: Lin
authors.affiliation: Department of Physics and Astronomy, Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln , Lincoln, Nebraska 68588-0511, United States.
authors.forename: Jingfeng
authors.initials: J
authors.lastname: Song
authors.affiliation: Department of Physics and Astronomy, Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln , Lincoln, Nebraska 68588-0511, United States.
authors.forename: Stephen
authors.initials: S
authors.lastname: Ducharme
authors.affiliation: School of Mechanical Engineering, Beijing Institute of Technology , Beijing 100081, China.
authors.forename: Lan
authors.initials: L
authors.lastname: Jiang
authors.affiliation: Institut de Chimie de la Matière Condensée de Bordeaux , Avenue du Docteur Albert Schweitzer Pessac F-33608 Cedex, France.
authors.forename: Jean-Francois
authors.initials: JF
authors.lastname: Silvain
authors.affiliation: Department of Electrical and Computer Engineering, University of Nebraska-Lincoln , Lincoln, Nebraska 68588-0511, United States.
authors.forename: Yongfeng
authors.initials: Y
authors.lastname: Lu
keywords: four-wave mixing; interlayer coupling; nonlinear optical imaging; second-harmonic generation; sum-frequency generation; transition metal dichalcogenides; van der Waals heterostructure