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1. Mott and generalized Wigner crystal states in WSe2/WS2 moiré superlattices

   https://doi.org/10.1038/s41586-020-2092-4  

   Regan, Emma C. ; Wang, Danqing ; Jin, Chenhao ; Bakti Utama, M. Iqbal ; Gao, Beini ; Wei, Xin ; Zhao, Sihan ; Zhao, Wenyu ; Zhang, Zuocheng ; Yumigeta, Kentaro ; et al ( March 2020 , Nature)
2. Observation of moiré excitons in WSe2/WS2 heterostructure superlattices

   https://doi.org/10.1038/s41586-019-0976-y  

   Jin, Chenhao ; Regan, Emma C. ; Yan, Aiming ; Iqbal Bakti Utama, M. ; Wang, Danqing ; Zhao, Sihan ; Qin, Ying ; Yang, Sijie ; Zheng, Zhiren ; Shi, Shenyang ; et al ( March 2019 , Nature)
3. Correlated insulating states at fractional fillings of the WS2/WSe2 moiré lattice

   https://doi.org/10.1038/s41567-021-01171-w  

   Huang, Xiong ; Wang, Tianmeng ; Miao, Shengnan ; Wang, Chong ; Li, Zhipeng ; Lian, Zhen ; Taniguchi, Takashi ; Watanabe, Kenji ; Okamoto, Satoshi ; Xiao, Di ; et al ( January 2021 , Nature Physics)
4. Filling Exciton Trap-States in Two-Dimensional Tungsten Disulfide (WS2) and Diselenide (WSe2) Monolayers

   https://doi.org/10.3390/nano11030770  

   Ezgi Eroglu, Zeynep ; Contreras, Dillon ; Bahrami, Pouya ; Azam, Nurul ; Mahjouri-Samani, Masoud ; Boulesbaa, Abdelaziz ( March 2021 , Nanomaterials)

   Two-dimensional transition metal dichalcogenides (2D-TMDs) hold a great potential to platform future flexible optoelectronics. The beating hearts of these materials are their excitons known as XA and XB, which arise from transitions between spin-orbit split (SOS) levels in the conduction and valence bands at the K-point. The functionality of 2D-TMD-based devices is determined by the dynamics of these excitons. One of the most consequential channels of exciton decay on the device functionality is the defect-assisted recombination (DAR). Here, we employ steady-state absorption and emission spectroscopies, and pump density-dependent femtosecond transient absorption spectroscopy to report on the effect of DAR on the lifetime of excitons in monolayers of tungsten disulfide (2D-WS2) and diselenide (2D-WSe2). These pump-probe measurements suggested that while exciton decay dynamics in both monolayers are driven by DAR, in 2D-WS2, defect states near the XB exciton fill up before those near the XA exciton. However, in the 2D-WSe2 monolayer, the defect states fill up similarly. Understanding the contribution of DAR on the lifetime of excitons and the partition of this decay channel between XA and XB excitons may open new horizons for the incorporation of 2D-TMD materials in future optoelectronics.
5. Deterministic Assembly of Arrays of Lithographically Defined WS2 and MoS2 Monolayer Features Directly From Multilayer Sources Into Van Der Waals Heterostructures

   https://doi.org/10.1115/1.4045259  

   Nguyen, Vu ; Gramling, Hannah ; Towle, Clarissa ; Li, Wan ; Lien, Der-Hsien ; Kim, Hyungjin ; Chrzan, Daryl C. ; Javey, Ali ; Xu, Ke ; Ager, Joel ; et al ( December 2019 , Journal of Micro and Nano-Manufacturing)

   Abstract One of the major challenges in the van der Waals (vdW) integration of two-dimensional (2D) materials is achieving high-yield and high-throughput assembly of predefined sequences of monolayers into heterostructure arrays. Mechanical exfoliation has recently been studied as a promising technique to transfer monolayers from a multilayer source synthesized by other techniques, allowing the deposition of a wide variety of 2D materials without exposing the target substrate to harsh synthesis conditions. Although a variety of processes have been developed to exfoliate the 2D materials mechanically from the source and place them deterministically onto a target substrate, they can typically transfer only either a wafer-scale blanket or one small flake at a time with uncontrolled size and shape. Here, we present a method to assemble arrays of lithographically defined monolayer WS2 and MoS2 features from multilayer sources and directly transfer them in a deterministic manner onto target substrates. This exfoliate–align–release process—without the need of an intermediate carrier substrate—is enabled by combining a patterned, gold-mediated exfoliation technique with a new optically transparent, heat-releasable adhesive. WS2/MoS2 vdW heterostructure arrays produced by this method show the expected interlayer exciton between the monolayers. Light-emitting devices using WS2 monolayers were also demonstrated, proving the functionality ofmore »the fabricated materials. Our work demonstrates a significant step toward developing mechanical exfoliation as a scalable dry transfer technique for the manufacturing of functional, atomically thin materials.« less