Spatially Dependent Electronic Structures and Excitons in a Marginally Twisted Moiré Superlattice of Spiral WS₂

Abstract

Twisted two-dimensional transition metal dichalcogenide (TMD) moirésuperlattices provide an additional degree of freedom to engineer electronic and optical properties. Nevertheless, controllable synthesis of marginally twisted homo TMD moireś uperlattices is still a challenge. Here, physical vapor deposition grown spiral WS 2 nanosheets are demonstrated to be a marginally twisted moirésuperlattice using scanning tunneling microscopy and spectroscopy. Periodic moirésuperlattices are found on the third layer (3L) and 4L of the spiral WS 2 nanosheet owing to the marginally twisted alignment between two neighboring layers, resulting in a highly localized flat band near the valence band maximum. Their bandgap depends on atomic stacking configurations, which gives a good interpretation for split moiréexcitons using photoluminescence at 77 K. This work can benefit the development of twisted homo TMD moirésuperlattices and could promote the profound research of twisted TMDs in the prospective field, such as strongly correlated physics and twistronics.

Understanding Dopant–Host Interactions on Electronic Structures and Optical Properties in Ce‐Doped WS2 Monolayers

“…The STS spectrum collected from the clean area exhibits a U shape, where the platform represents the bandgap, consistent with the previous reports. [36,42,43] While for the STS spectrum collected at the Ce W , there are four defect states in the bandgap, labeled as A, B, C, and D with energy levels of ≈0.76, 0.70, 0. First-principles DFT calculations were carried out to further confirm the attribution of Ce W and the electronic structures of the monolayer Ce-WS 2 , and the corresponding atomic model of a 5 × 5 × 1 supercell is shown in Figure S3 of the Supporting Information.…”

“…The STS spectrum collected from the clean area exhibits a U shape, where the platform represents the bandgap, consistent with the previous reports. [ 36,42,43 ] While for the STS spectrum collected at the Ce W , there are four defect states in the bandgap, labeled as A, B, C, and D with energy levels of ≈0.76, 0.70, 0.40, and −1.40 eV relative to the Fermi level respectively.…”

Localization-enhanced second harmonic generation in twisted WS2 spirals

“…Another interesting observation is that the onset of SHG decline region changes from Region 3 to Region 2 to Region 1 as the twisted angle increases from 13º to 16º to 20º, respectively. Overall, depending on the twisted angles and layers, the SHG signal can be ampli ed 12-136 times for ≈ 0º spirals 29,30 , 4-92 times for 13º spirals, 10-42 times for 16º spirals, and 4-26 times for 20º spirals, respectively (Table 1). Both the maximum and minimum enhancement factors decrease with increasing twisted angles.…”

Twist-angle-dependent momentum-space direct and indirect interlayer excitons in WSe2/WS2 heterostructure

“…[1][2][3][4][5][6] van der Waals (vdW) heterostructures formed by stacking different TMDCs have further emerged as a new powerful tool for exploring new excitonic phenomena with designed functionalities, especially in the so-called type-II band alignment, wherein the conduction band minimum (CBM) and the valence band maximum (VBM) are in different layers. [7][8][9][10][11][12] In the vdW heterostructures with type-II band alignment, spatially indirect interlayer excitons can be formed with electrons and holes localized in different TMDC layers with much longer lifetimes and 13,14 valley depolarization time 15 than those of spatially direct intralayer excitons, thereby allowing ultrafast charge transfer [16][17][18] and ultra-long-range exciton diffusion. 19 Meanwhile, the lattice mismatch and rotational misalignment in the heterostructure are predicted to strongly inuence interlayer coupling, 12,[20][21][22][23][24] which suggests the possibility of regulating the interlayer excitons by simply varying the twist angles.…”

“…[7][8][9][10][11][12] In the vdW heterostructures with type-II band alignment, spatially indirect interlayer excitons can be formed with electrons and holes localized in different TMDC layers with much longer lifetimes and 13,14 valley depolarization time 15 than those of spatially direct intralayer excitons, thereby allowing ultrafast charge transfer [16][17][18] and ultra-long-range exciton diffusion. 19 Meanwhile, the lattice mismatch and rotational misalignment in the heterostructure are predicted to strongly inuence interlayer coupling, 12,[20][21][22][23][24] which suggests the possibility of regulating the interlayer excitons by simply varying the twist angles.…”