Strain Engineering on the Electronic and Optical Properties of WSSe Bilayer

Pressure-Driven Structural and Electronic Transitions in a Two-Dimensional Janus WSSe Crystal

In this work, we presented the first report on the high-pressure structural stability and electrical transport characteristics in WSSe under different hydrostatic environments through Raman spectroscopy, electrical conductivity, and high-resolution transmission electron microscopy (HRTEM) coupled with first-principles theoretical calculations. For nonhydrostatic conditions, WSSe endured a phase transition at 15.2 GPa, followed by a semiconductor-to-metal crossover at 25.3 GPa. Furthermore, the bandgap closure was accounted for the metallization of WSSe as derived from theoretical calculations. Under hydrostatic conditions, ∼ 2.0 GPa pressure hysteresis was detected for the emergence of phase transition and metallization in WSSe because of the feeble deviatoric stress. Upon depressurization, the reversibility of the phase transition was substantiated by those of microscopic HRTEM observations under different hydrostatic environments. Our high-pressure investigation on WSSe advances the insightful understanding of the crystalline structure and electronic properties for the Janus transition-metal dichalcogenide (TMD) family and boosts prospective developments in functional devices.

High throughput calculations for a dataset of bilayer materials

Bilayer materials made of 2D monolayers are emerging as new systems creating diverse opportunities for basic research and applications in optoelectronics, thermoelectrics, and topological science among others. Herein, we present a computational bilayer materials dataset containing 760 structures with their structural, electronic, and transport properties. Different stacking patterns of each bilayer have been framed by analyzing their monolayer symmetries. Density functional theory calculations including van der Waals interactions are carried out for each stacking pattern to evaluate the corresponding ground states, which are correctly identified for experimentally synthesized transition metal dichalcogenides, graphene, boron nitride, and silicene. Binding energies and interlayer charge transfer are evaluated to analyze the interlayer coupling strength. Our dataset can be used for materials screening and data-assisted modeling for desired thermoelectric or optoelectronic applications.

Strain-induced ultrahigh power conversion efficiency in BP-MoSe2vdW heterostructure

Photocatalytic water splitting is a promising method for hydrogen production, and the search for efficient photocatalysts has received extensive attention. Two-dimensional van der Waals (vdW) heterostructures have recently been considered excellent candidates for photocatalytic water splitting. In this work, a BP-MoSe₂vdW heterostructure composed of a blue phosphorus (BP) and MoSe₂monolayer was studied as a potential photocatalyst for water splitting using first-principles calculations. The results show that the heterostructure has a type-II band structure, and the band edges straddle water redox potentials under biaxial strains from -3% to 2%, satisfying the requirements for photocatalytic water splitting. In addition, the heterostructure has excellent power conversion efficiency (PCE) and strong optical absorption in both visible light and near-ultraviolet region, indicating that it is a very promising candidate for photocatalytic water splitting. Specifically, the PCE was enhanced to ∼20.2% under a tensile strain of 2%. The Gibbs free energy profiles indicate that BP-MoSe₂vdW heterostructure exhibits good catalytic performance in hydrogen and oxygen evolution reactions. In particular, high carrier mobility implies that the transfer of carriers to reactive sites is easy, and the recombination probability of photogenerated electron-hole pairs is reduced.

Electronic structure of strain-tunable Janus WSSe–ZnO heterostructures from first-principles

The electronic structure of semiconducting 2D materials such as monolayer transition metal dichalcogenides (TMDs) are known to be tunable via environment and external fields, and van der Waals (vdW) heterostructures consisting of stacks of distinct types of 2D materials offer the possibility to further tune and optimize the electronic properties of 2D materials. In this work, we use density functional theory (DFT) calculations to calculate the structure and electronic properties of a vdW heterostructure of Janus monolayer WSSe with monolayer ZnO, both of which possess out of plane dipole moments. The effects of alignment, biaxial and uniaxial strain, orientation, and electric field on dipole moments and band edge energies of this heterostructure are calculated and examined. We find that the out of plane dipole moment of the ZnO monolayer is highly sensitive to strain, leading to the broad tunability of the heterostructure band edge energies over a range of experimentally-relevant strains. The use of strain-tunable 2D materials to control band offsets and alignment is a general strategy applicable to other vdW heterostructures, one that may be advantageous in the context of clean energy applications, including photocatalytic applications, and beyond.

Using strain engineering to optimize novel heterostructure materials to produce hydrogen from water.

Tuning the physical properties of ultrathin transition-metal dichalcogenides via strain engineering

Transition-metal dichalcogenides (TMDs) have become one of the recent frontiers and focuses in two-dimensional (2D) materials fields thanks to their superior electronic, optical, and photoelectric properties. Triggered by the growing demand for developing nano-electronic devices, strain engineering of ultrathin TMDs has become a hot topic in the scientific community. In recent years, both theoretical and experimental research on the strain engineering of ultrathin TMDs have suggested new opportunities to achieve high-performance ultrathin TMDs based devices. However, recent reviews mainly focus on the experimental progress and the related theoretical research has long been ignored. In this review, we first outline the currently employed approaches for introducing strain in ultrathin TMDs, both their characteristics and advantages are explained in detail. Subsequently, the recent research progress in the modification of lattice and electronic structure, and physical properties of ultrathin TMDs under strain are systematically reviewed from both experimental and theoretical perspectives. Despite much work being done in this filed, reducing the distance of experimental progress from the theoretical prediction remains a great challenge in realizing wide applications of ultrathin TMDs in nano-electronic devices.