Two-dimensional (2D) ReSe2 has attracted considerable interest due to its unique anisotropic mechanical, optical, and exitonic characteristics. Recent transient absorption experiments demonstrated a prolonged lifetime of photoexcited charge carriers by stacking ReSe2 with MoS2, but the underlying mechanism remains elusive. Here, by combining time-domain density functional theory with nonadiabatic molecular dynamics, we investigate the electronic properties and charge carrier dynamics of 2D ReSe2/MoS2 van der Waals (vdW) heterostructure. ReSe2/MoS2 has a type II band alignment that exhibits spatially distinguished conduction and valence band edges, and a built-in electric field is formed due to interface charge transfer. Remarkably, in spite of the decreased band gap and increased decoherence time, we demonstrate that the photocarrier lifetime of ReSe2/MoS2 is ∼5 times longer than that of ReSe2, which originates from the greatly reduced nonadiabatic coupling that suppresses electron–hole recombination, perfectly explaining the experimental results. These findings not only provide physical insights into experiments but also shed light on future design and fabrication of functional optoelectronic devices based on 2D vdW heterostructures.

Construction of tunable and robust two-dimensional (2D) molecular arrays with desirable lattices and functionalities over a macroscopic scale relies on spontaneous and reversible noncovalent interactions between suitable molecules as building blocks. Halogen bonding, with active tunability of direction, strength, and length, is ideal for tailoring supramolecular structures. Herein, by combining low-temperature scanning tunneling microscopy and systematic first-principles calculations, we demonstrate novel halogen bonding involving single halogen atoms and phase engineering in 2D molecular self-assembly. On the Au(111) surface, we observed catalyzed dehalogenation of hexabromobenzene (HBB) molecules, during which negatively charged bromine adatoms (Br) were generated and participated in assembly via unique C-Br···Br interaction, drastically different from HBB assembly on a chemically inert graphene substrate. We successfully mapped out different phases of the assembled superstructure, including densely packed hexagonal, tetragonal, dimer chain, and expanded hexagonal lattices at room temperature, 60 °C, 90 °C, and 110 °C, respectively, and the critical role of Br in regulating lattice characteristics was highlighted. Our results show promise for manipulating the interplay between noncovalent interactions and catalytic reactions for future development of molecular nanoelectronics and 2D crystal engineering.

By combining density functional theory with low-energy effective Hamiltonian, we demonstrate strain-engineered electronic and topological properties of the recently synthesized two-dimensional (2D) bismuthene on SiC(0001) substrate. As bismuthene on SiC(0001) exhibits an indirect gap of 0.62 eV with nontrivial topology, we show that the band gap size can be further increased by an applied tensile strain, which follows a nearly linear fashion. Especially, with a tensile strain of 7%, the topological gap can be enhanced to an unprecedented value of 0.83 eV, originating from the different deformation potentials of the conduction band minimum principally contributed from p orbitals of Bi and valance band maximum from the hybridized states of Bi overlayer and SiC substrate. Moreover, we discuss the strength of spin–orbit coupling, in additional to the strain effect, in tuning the electronic structures and topological edge states. Our results suggest the promise of strain engineering in manipulating large-gap quantum spin Hall states on conventional semiconductor for practical dissipationless electronic transport and quantum information processing.

Recent years have witnessed a surge of research in twodimensional (2D) ferroelectric structures that may circumvent the depolarization effect in conventional perovskite oxide films. Herein, by first-principles calculations, we predict that an orthorhombic phase of lead(II) oxide, PbO, serves as a promising candidate for 2D ferroelectrics with good stability. With a semiconducting nature, 2D ferroelectric PbO exhibits intrinsic valley polarization, which leads to robust ferroelectricity with an in-plane spontaneous polarization of 2.4 × 10 −10 C/m and a Curie temperature of 455 K. Remarkably, we reveal that the ferroelectricity is strain-tunable, and ferroelasticity coexists in the PbO film, implying the realization of 2D multiferroics. The underlying physical mechanism is generally applicable and can be extended to other oxide films such as ferroelectric SnO and GeO, thus paving an avenue for future design and fabrication of functional ultrathin devices that are compatible with Si-based technology.

Quantum spin Hall to quantum anomalous Hall phase transition in monolayer jacutingaite (Pt2HgSe3) induced by chalogen (S, Se, Te) functionalization.