The interlayer coupling in van der Waals (vdW) crystals has substantial effects on the performance of materials. However, an in-depth understanding of the microscopic mechanism on the defect-modulated interlayer coupling is often elusive, owing partly to the challenge of atomic-scale characterization. Here we report the native Se-vacancies in a charge-density-wave metal 2H-NbSe₂, as well as their influence on the local atomic configurations and interlayer coupling. Our low-temperature scanning tunneling microscopy (STM) measurements, complemented by density functional theory calculations, indicate that the Se-vacancies in few-layer NbSe₂ can generate obvious atomic distortions due to the Jahn–Teller effect, thus breaking the rotational symmetry on the nanoscale. Moreover, these vacancies can locally generate an in-gap state in single-layer NbSe₂, and more importantly, lead to a colossal suppression of interlayer coupling in the bilayer system. Our results provide clear structural and electronic fingerprints around the vacancies in vdW crystals, paving the way for developing functional vdW devices.

Grain boundaries in two-dimensional (2D) semiconductors generally induce distorted band alignment and interfacial charge, which impair their electronic properties for device applications. Here, we report the improvement of band alignment at the grain boundaries of PtSe₂, a 2D semiconductor, with selective adsorption of a presentative organic acceptor, tetracyanoquinodimethane (TCNQ). TCNQ molecules show selective adsorption at the PtSe₂ grain boundary with strong interfacial charge. The adsorption of TCNQ distinctly improves the band alignment at the PtSe₂ grain boundaries. With the charge transfer between the grain boundary and TCNQ, the local charge is inhibited, and the band bending at the grain boundary is suppressed, as revealed by the scanning tunneling microscopy and spectroscopy (STM/S) results. Our finding provides an effective method for the advancement of the band alignment at the grain boundary by functional molecules, improving the electronic properties of 2D semiconductors for their future applications.

Two-dimensional (2D) honeycomb-like materials have been widely studied due to their fascinating properties. In particular, 2D honeycomb-like transition metal monolayers, which are good 2D ferromagnet candidates, have attracted intense research interest. The honeycomb-like structure of hafnium, hafnene, has been successfully fabricated on the Ir(111) substrate. However, its electronic structure has not yet been directly elucidated. Here, we report the electronic structure of hafnene grown on the Ir(111) substrate using angle-resolved photoemission spectroscopy (ARPES). Our results indicate that the presence of spin-orbit coupling and Hubbard interaction suppresses the earlier predicted Dirac cones at the K points of the Brillouin zone. The observed band structure of hafnene near the Fermi level is very simple: an electron pocket centered at the Γ point of the Brillouin zone. This electron pocket shows typical parabolic dispersion, and its estimated electron effective mass and electron density are approximately 1.8 m_e and 7 × 10¹⁴ cm⁻², respectively. Our results demonstrate the existence of 2D electron gas in hafnene grown on the Ir(111) substrate and therefore provide key information for potential hafnene-based device applications.

Tomonaga–Luttinger liquid (TLL), a peculiar one-dimensional (1D) electronic behavior due to strong correlation, was first studied in 1D nanostructures and has attracted significant attention over the last several decades. With the rise of new two-dimensional (2D) quantum materials, 1D nanostructures in 2D materials have provided a new platform with a well-defined configuration at the atomic scale for studying TLL electronic behavior. In this paper, we review the recent progress of TLL electronic features in emerging 2D materials embedded with various 1D nanostructures, including island edges, domain walls, and 1D moiré patterns. Specifically, novel physical phenomena, such as 1D edge states in 2D transition metal dichalcogenides (TMDs), helical TLL in 2D topological insulators (2DTI), and chiral TLL in 2D quantum Hall systems, are described and discussed at the nanoscale. We also analyze challenges and opportunities at the frontier of this research area.

With the unique properties, layered transition metal dichalcogenide (TMD) and its heterostructures exhibit great potential for applications in electronics. The electrical performance, e.g., contact barrier and resistance to electrodes, of TMD heterostructure devices can be significantly tailored by employing the functional layers, called interlayer engineering. At the interface between different TMD layers, the dangling-bond states normally exist and act as traps against charge carrier flow. In this study, we propose a technique to suppress such carrier trap that uses enhanced interlayer hybridization to saturate dangling-bond states, as demonstrated in a strongly interlayer-coupled monolayer-bilayer PtSe₂ heterostructure. The hybridization between the unsaturated states and the interlayer electronic states of PtSe₂ significantly reduces the depth of carrier traps at the interface, as corroborated by our scanning tunnelling spectroscopic measurements and density functional theory calculations. The suppressed interfacial trap demonstrates that interlayer saturation may offer an efficient way to relay the charge flow at the interface of TMD heterostructures. Thus, this technique provides an effective way for optimizing the interface contact, the crucial issue exists in two-dimensional electronic community.