Transition-metal dichalcogenides (TMDs) are promising materials for optoelectronic devices. Their lattice and electronic structural evolutions under high strain conditions and their relations remain open questions. We exert pressure on WS monolayers on different substrates, namely, Si/SiO substrate and diamond anvil surface up to ∼25 GPa. Structural distortions in various degree are disclosed based on the emergence of Raman-inactive B mode. Splits of out-of-plane B and A' modes are only observed on Si/SiO substrate due to extra strain imported from volume decrease in Si and corrugation of SiO surface, and its photoluminescence (PL) quenches quickly because of decreased K-K transition by conspicuous distortion of Brillouin zone. While diamond anvil surface provides better hydrostatic environment, combined analysis of PL and absorption proves that pressure effectively tunes PL emission energy and enhances Coulomb interactions. Knowledge of these distinct pressure tunable characteristics of monolayer WS improves further understanding of structural and optical properties of TMDs.

Vertical heterostructures (HSs) constructed with two-dimensional (2D) materials is expected to generate fascinating properties due to interlayer coupling between neighboring layers. However, interlayer coupling can be easily obscured by cross-contamination during transfer processes, rendering their experimental demonstration challenging. Here, we explore the coupling-assisted renormalization of excitons and vibrations in a mechanically fabricated MoSe2–WSe2 HS through high-pressure photoluminescence, Raman spectra, and density functional theory calculations. Accompanied by the interlayer coupling enhancement, the excitonic and vibrational renormalizations involving dimensionality and composition variations were achieved. A cycle of 2D–3D–2D excitonic evolution was disclosed and pressure-induced emergence of X– exciton of MoSe2 in HS was found reflecting the band structure transition in the MoSe2–WSe2 HS. The Raman spectra reveals that the coupled A2″ vibrations of WSe2 and MoSe2 in HS was stiffened and out-of-plane A1′ vibrations of WSe2 and MoSe2 in HS got coherent upon pressure modulation. This coupling-assisted renormalization in MoSe2–WSe2 HS can be extended to other 2D layered HSs, which indicates the possibility to design a flexible HS with controlled excitonic and vibrational system for light-emitting diodes, excitonic, and photovoltaic devices.

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Pressure engineering is considered as a novel strategy to modulate the properties of transition metal dichalcogenide materials. Here, through photoluminescence (PL) and Raman measurements, we investigate the electronic band structure variation and lattice vibrational dynamics of monolayer tungsten diselenide (WSe2) under pressure. As the pressure increases, the energy of the direct Κ→Κ interband transition increases, whereas that of the indirect Λ→Κ interband transition decreases, leading to a significant transition from direct to indirect band gap at 3.8 GPa. With the increase of pressure, the intensity of the direct Κ→Κ interband transition constantly decreases and finally vanishes around 12.2 GPa. Moreover, a remarkable transition between A′ and LA(M) modes under pressure has been determined by virtue of Raman spectra variations, which indicate a pressure‐induced lattice disorder. This work provides a deep understanding of the intrinsic variation of WSe2 under pressure, which effectively facilitates the development of device applications.

High-pressure investigations on transition-metal dichalcogenides (TMD) have been considered as an efficient way to investigate their unique crystalline and electronic properties. Here we studied the vibrational behaviors of pressurized multilayer WSe 2 with two (2TL) to six layers (6TL) by Raman spectroscopy. The intralayer and interlayer vibrations of WSe 2 all show a monotonous blue shift without any discontinuity. Due to the strong interlayer coupling interactions, no structural transition occurs, but nondegeneration splitting of shear mode vibrations coming from pressure-induced in-plane deformation is observed. As the interlayer coupling increases in thicker WSe 2 , the in-plane deformation is suppressed and takes place at higher pressure. The monotonous increase of force constants and elastic constants suggested a stable structure of WSe 2 within our studied pressure range.