Structural regulation and application of transition metal dichalcogenide monolayers: Progress and challenges

Quantum confinement effects and structures with broken inversion symmetry distinguish transition metal halide (TMD) monolayers from their bulk equivalents in several ways, for instance, indirect-to-direct band gap transitions, reduced surrounding dielectrics, ferromagnetism, valley selectivity and the regulation of the valley degrees of freedom. Therefore, many excellent physical and chemical properties have been obtained, and two-dimensional (2D) TMD monolayers have sparked extensive interest in the fields of catalysis, optoelectronics, magnetism, and quantum devices. TMD monolayers have 100% exposed atoms, so their electronic structure is easily regulated. The functional development and utilization of monolayer TMDs are leading to remarkable breakthroughs. In this paper, the recent research advancements regarding the electronic structure regulation and application of 2D TMD monolayers have been summarized, including their unique structural characteristics, electronic structure regulation strategies, and typical applications. This review also presents the current challenges of 2D TMD monolayers, including the preparation and processing of large-scale 2D monolayer materials, the design of specific materials, and the introduction of theoretical calculations. The future development of 2D TMD monolayers is predicted, especially in the field of biomedical engineering. This work will help guide researchers design single-layer 2D materials with unique properties and gain an in-depth understanding of their applications in energy, magnetism, optics, biomedicine, and other fields.