The van der Waals (vdW) heterostructures have rich functions and intriguing physical properties, which has attracted wide attention. Effective control of excitons in vdW heterostructures is still urgent for fundamental research and realistic applications. Here, we successfully achieved quantitative tuning of the intralayer exciton of monolayers and observed the transition from intralayer excitons to interlayer excitons in WS 2 / MoSe 2 heterostructures, via hydrostatic pressure. The energy of interlayer excitons is in a "locked" or "superstable" state, which is not sensitive to pressure. The first-principles calculation reveals the stronger interlayer interaction which leads to enhanced interlayer exciton behavior in WS 2 / MoSe 2 heterostructures under external pressure and reveals the robust peak of interlayer excitons. This work provides an effective strategy to study the interlayer interaction in vdW heterostructures and reveals the enhanced interlayer excitons in WS 2 /MoSe 2 , which could be of great importance for the material and device design in various similar quantum systems.

An experimental study on the effect of hexagonal boron nitride (h‐BN) underlay and cap layers on excitonic dynamics in monolayer WS2 is reported. A monolayer WS2 flake is fabricated by mechanical exfoliation. By using a dry transfer technique, three regions of the sample are obtained: WS2 directly on SiO2, WS2 on h‐BN, and WS2 sandwiched by two h‐BN flakes. Photoluminescence measurements show higher yield and narrower linewidth of the h‐BN/WS2/h‐BN region. Transient absorption measurements reveal that the top h‐BN layer enhances the exciton formation, prolongs the exciton lifetime, and slightly affects the exciton–exciton annihilation. By performing spatially resolved transient absorption measurements, exciton diffusion coefficients of about 100, 40, and 26 cm2 s−1 for the regions of WS2, h‐BN/WS2, and h‐BN/WS2/h‐BN, respectively, are obtained. The suppression of exciton diffusion by h‐BN is attributed to the additional phonon scattering mechanisms introduced by h‐BN, which decreases the exciton mean free path and thus the diffusion coefficient. The findings provide useful information for designing and understanding the effect of h‐BN layers interfacing with 2D semiconductors.

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Hot charge-transfer excitons are formed in a transition metal dichalcogenide trilayer heterostructure and diffuse during their cooling process.

Using a gas separation membrane as a simple gas separation device has an obvious advantage because of the low energy consumption and pollution-free manufacturing. The first-principles calculations used in this work show that germanene with its divacancy is an excellent material for use as a hydrogen (H) and helium (He) separation membrane, and that it displays an even better competitive advantage than porous graphene and porous silicene. Porous germanene with its divacancy is chemically inert to gas molecules, because it lacks additional atoms to protect the edged dangling germanium atoms in defects, and thus shows great advantages for gas separation over previously prepared graphene. The energy barriers to H and He penetrating porous germanene are quite low, and the permeabilities to H and He are high. Furthermore, the selectivities of porous germanene for H and He relative to other gas molecules are high, up to 10 and 10, respectively, which are superior to those of porous graphene (10) and porous silicene (10); thus the separation efficiency of porous germanene is much higher than that of porous graphene and porous silicene. Therefore, germanene is a favorable candidate as a gas separation membrane material. At the same time, the successful synthesis of germanene in the laboratory means that it is possible to use it in real applications.