Extraordinary Phonon Displacement and Giant Resonance Raman Enhancement in WSe₂/WS₂ Moiré Heterostructures

Abstract

Twisted van der Waals heterostructures are known to induce surprisingly diverse and intriguing phenomena, such as correlated electronic phase and unconventional optical properties. This can be realized by controlled rotation of adjacent atomic planes, which provides an uncommon way to manipulate inelastic light–matter interactions. Here, we discover an extraordinary blue shift of 5–6 wavenumbers for high-frequency phonon modes in WS2/WSe2 twisted heterobilayers, captured meticulously using Raman spectroscopy. Phonon spectra displace rapidly over a subtle change in interlayer twist angle owing to heterostrain and atomic reconstruction from the Moiré pattern. First-order linear coefficients of the phonon modes in twisted heterostructures are further found to increase largely compared to their monolayer counterpart and vary immensely with the twist angle. Exceptional and extravagant enhancement of up to 50-fold is observed in the Raman vibrational intensity at a specific twist angle; this is largely influenced by the resonance process derived from a simple critical twist angle model. In addition, we depict how the resonance can be modulated by changing the thermal conditions and also the stacking angle. Therefore, our work further highlights the twist-driven phonon dynamics in pristine two-dimensional heterostructures, adding vital insight into Moiré physics and promoting comprehensive understanding of structural and optical properties in Moiré superlattices.

The effects of intercalated environmental gas molecules on carrier dynamics in WSe2/WS2heterostructures

“…65–68 According to previous study, the WSe 2 /WS 2 vdW heterostructure with C7 stacking is the most stable configuration. 35,37,38,65,69,70 Thus, we focus on C7 configuration in this study, while our test calculations on other geometries like T stacking demonstrate that molecule intercalation would not change the sequence of energies for the bilayer heterostructures. In order to reduce the lattice mismatch, the lattice constant of the WSe 2 /WS 2 heterostructure is set to be the average value of the lattice constants of WSe 2 and WS 2 .…”

“…[23][24][25][26] Due to the robust type-II band alignment, WSe 2 /WS 2 vdW heterostructure has attracted considerable attention. [27][28][29][30][31][32][33][34][35][36][37][38] In vertical heterostructures, the vdW gap between monolayer components offers space for the intercalation of ions and molecules, thereby giving rise to new opportunities for property modulation. It has been evidenced that ion intercalation into TMD heterostructures has a significant impact on the chemical and physical properties and leads to broad applications in energy storage.…”

“…23–26 Due to the robust type-II band alignment, WSe 2 /WS 2 vdW heterostructure has attracted considerable attention. 27–38…”

Twisted van der Waals Quantum Materials: Fundamentals, Tunability, and Applications

“…Furthermore, the researchers also concluded that twist angle can lead to a large enhancement in Raman vibrational intensity which has been demonstrated for the first time in TMD heterostructures. 382 Moiréphonons exhibit a high degree of complexity, challenging to attribute specific peaks to phonons in bilayer TMDs. This complexity is further compounded in the case of folded modes, which are highly influenced by moirésuperlattices.…”

Self‐Assembly of Mixed‐Dimensional GeS1−xSex (1D Nanowire)–(2D Plate) Van der Waals Heterostructures

“…[5,6] The advent of 2D materials eliminated many of these compatibility constraints, [7] with micromechanical stacking allowing the integration of 2D crystals with different structures and large lattice mismatch [8,9] and opening up additional degrees of freedom such as interlayer twist. [10][11][12] Different 2D [13][14][15][16] and thicker van der Waals crystals [17,18] can also be stitched into lateral heterostructures with covalent interfaces embedded in each of the layers. [19] Heterostructures have also been formed from low-dimensional structures, notably nanowires where both the axial [20][21][22][23] and radial [24,25] integration of different materials has been demonstrated.…”