Dopants and grain boundary effects in monolayer MoS2: a first-principles study

Recent progress in 2D hybrid heterostructures from transition metal dichalcogenides and organic layers: properties and applications in energy and optoelectronics fields

Atomically thin transition metal dichalcogenides (TMDs) present extraordinary optoelectronic, electrochemical, and mechanical properties that have not been accessible in bulk semiconducting materials. Recently, a new research field, 2D hybrid heteromaterials, has emerged upon integrating TMDs with molecular systems, including organic molecules, polymers, metal-organic frameworks, and carbonaceous materials, that can tailor the TMD properties and exploit synergetic effects. TMD-based hybrid heterostructures can meet the demands of future optoelectronics, including supporting flexible, transparent, and ultrathin devices, and energy-based applications, offering high energy and power densities with long cycle lives. To realize such applications, it is necessary to understand the interactions between the hybrid components and to develop strategies for exploiting the distinct benefits of each component. Here, we provide an overview of the current understanding of the new phenomena and mechanisms involved in TMD/organic hybrids and potential applications harnessing such valuable materials in an insightful way. We highlight recent discoveries relating to multicomponent hybrid materials. Finally, we conclude this review by discussing challenges related to hybrid heteromaterials and presenting future directions and opportunities in this research field.

Structural engineering brings new electronic properties to Janus ZrSSe and HfSSe monolayers

Interfacing effects within emergent two-dimensional (2D) materials are of fundamental interest and are at the center of applications in nanoelectronics. Thus, out-of-plane and in-plane heterostructures as well as electronic heterostructures with phase boundaries and large-angle (60°) grain boundaries (GBs) of Janus ZrSSe and HfSSe are studied in this work using first-principles calculations. The out-of-plane heterostructures of T-ZrSSe and T-HfSSe illustrate quite weak interfacing interactions, thus the electronic properties are, unusually, more like the superposition of individual monolayers. The in-plane heterostructures of T-ZrSSe and T-HfSSe, interestingly, exhibit an indirect-direct band gap transition and type-II band alignment, which correspond to boosted optical properties and spatially separated excitons. For the in-plane electronic heterostructures that are constituted by T-ZrSSe and H-ZrSSe, semiconductor-metal crossover occurs due to the polar discontinuity across the T-H phase boundary, and they behave as one-dimensional metallic wires embedded in otherwise semiconducting Janus ZrSSe, creating a one-dimensional electron/hole gas. This also indicates a strategy for stabilizing the unstable and/or metastable monolayer via the phase boundary. As a result of the zero formal bulk polarization of the T-phase ZrSSe, the metallicity of 60° GBs originates mainly from the edge atoms rather than from the polar discontinuity.

Tuning MoSO monolayer properties for optoelectronic and spintronic applications: effect of external strain, vacancies and doping

Since the successful synthesis of the MoSSe monolayer, two-dimensional (2D) Janus materials have attracted huge attention from researchers. In this work, the MoSO monolayer with tunable electronic and magnetic properties is comprehensively investigated using first-principles calculations based on density functional theory (DFT). The pristine MoSO single layer is an indirect gap semiconductor with energy gap of 1.02(1.64) eV as predicted by the PBE(HSE06) functional. This gap feature can be efficiently modified by applying external strain presenting a decrease in its value upon switching the strain from compressive to tensile. In addition, the effects of vacancies and doping at Mo, S, and O sites on the electronic structure and magnetic properties are examined. Results reveal that Mo vacancies, and Al and Ga doping yield magnetic semiconductor 2D materials, where both spin states are semiconductors with significant spin-polarization at the vicinity of the Fermi level. In contrast, single S and O vacancies induce a considerable gap reduction of 52.89% and 58.78%, respectively. Doping the MoSO single layer with F and Cl at both S and O sites will form half-metallic 2D materials, whose band structures are generated by a metallic spin-up state and direct gap semiconductor spin-down state. Consequently, Mo_V, Mo_Al, Mo_Ga, S_F, S_Cl, O_F, and O_Cl are magnetic systems, and the magnetism is produced mainly by the Mo transition metal that exhibits either ferromagnetic or antiferromagnetic coupling. Our work may suggest the MoSO Janus monolayer as a prospective candidate for optoelectronic applications, as well as proposing an efficient approach to functionalize it to be employed in optoelectronic and spintronic devices.

Atomic structure and stability analysis of the MoSO Janus monolayer.