Spectroscopic Signatures for Interlayer Coupling in MoS₂–WSe₂ van der Waals Stacking

Abstract

Stacking of MoS 2 and WSe 2 monolayers is conducted by transferring triangular MoS 2 monolayers on top of WSe 2 monolayers, all grown by chemical vapor deposition (CVD).Raman spectroscopy and photoluminescence (PL) studies reveal that these mechanically stacked monolayers are not closely coupled, but after a thermal treatment at 300 °C, it is possible to produce van der Waals solids consisting of two interacting transition metal dichalcogenide (TMD) monolayers. The layer-number sensitive Raman out-of-plane mode A 2 1g for WSe 2 (309 cm À1 ) is found sensitive to the coupling between two TMD monolayers. The presence of interlayer excitonic emissions and the changes in other intrinsic Raman modes such as E 00 for MoS 2 at 286 cm À1 and A 2 1g for MoS 2 at around 463 cm À1 confirm the enhancement of the interlayer coupling.

Anomalous Light Cones and Valley Optical Selection Rules of Interlayer Excitons in Twisted Heterobilayers

“…The second and third terms describe respectively the light coupling mediated by bright intralayer exciton X τ in MoX 2 layer through hole interlayer hopping, and X τ in WX 2 through electron hopping. E M and E W are the energies of the intralayer excitons, a few hundred meV above E I as determined from optical and scanning tunneling measurements [19][20][21]30]. D τ τ,Q can be extracted from ab initio calculations at several commensurate stackings [40], from which we can determine the dipole strength, and the ellipticity and major axes of the emission polarization of the six-fold light cones at a general twist angle.…”

“…MoX 2 /WX 2 (X=Se, S) heterobilayers have been realized [19][20][21][22][23][24][25], which feature a type-II band alignment with the conduction (valence) band edges located in MoX 2 (WX 2 ) layer. Exciton then has the lowest energy in an interlayer configuration (i.e.…”

“…Exciton then has the lowest energy in an interlayer configuration (i.e. electron and hole in different layers), from which luminescence is observed [19][20][21]. Due to the spatially indirect nature, interlayer excitons in MoSe 2 /WSe 2 heterobilayers have shown long lifetime exceeding nanosecond, repulsive interaction, and electrostatically tunable resonance [19], all of which are highly desirable for the realization of excitonic circuits and condensation [26][27][28][29].…”

Vibrational and optical properties of MoS2: From monolayer to bulk

“…However, band gaps are different enough to generate band mismatch in heterostructures. We can combine TMDs in vertical heterostructures for quantum well growth [49,173,194], with the purpose of selective confinement of photogenerated excitons. Figure 22 shows the BSE spectra of single-layer MoSe 2 , WS 2 , and WSe 2 (solid lines) and the RPA spectra (dashed lines).…”

Influence of the substrate material on the optical properties of tungsten diselenide monolayers

“…In prior studInfluence of the substrate material on the optical properties of tungsten diselenide monolayers 2 S Lippert et al ies on WSe 2 , layers were deposited on SiO 2 /Si substrates [41,42], sapphire [43,44], graphene [45], and fused silica (quartz) [34,46] or sandwiched between layers of hBN [47]. Based on the literature on WSe 2 and its properties, it has been identified as an ideal/ suitable testbed for investigating the impact of substrate properties on its excitonic species.…”