Atomic stacking restores light emission in bilayer 2D semiconductors

Researchers at National Cheng Kung University (NCKU) have advanced the study of two-dimensional (2D) semiconductors by achieving precise control over the atomic stacking of bilayer molybdenum disulfide (MoS₂). Using chemical vapor deposition (CVD), the team synthesized a unique 1H-stacked MoS₂ bilayer, which overcomes the indirect-bandgap limitations of conventional bilayers, enabling a direct bandgap and enhanced valley polarization properties. These findings were published in the October 1, 2026 issue of Nature.

The research, led by Dr. Kuang-I Lin and involving multiple institutions, highlights the potential of 2D materials like MoS₂ in next-generation semiconductor devices. MoS₂, known for its semiconducting properties, is part of the 2D materials family, which includes graphene. These materials are characterized by atomic-scale thickness and unique electronic and optical properties, making them promising candidates for future semiconductor technologies.

The study demonstrated that controlling atomic stacking can modify the electronic band structure of bilayer materials, enabling direct-bandgap characteristics and improved optical properties. The team employed a two-step CVD growth strategy and rapid quenching to achieve the 1H stacking configuration, which has been challenging to obtain in a stable form.

To validate the atomic stacking and its physical properties, the researchers used a combination of techniques, including atomic-resolution scanning transmission electron microscopy (STEM), electron diffraction, second-harmonic generation (SHG), photoluminescence (PL), density functional theory (DFT) calculations, and angle-resolved photoemission spectroscopy (ARPES). These methods provided comprehensive evidence of the material's atomic structure, electronic band structure, and optical properties.

The results showed that the 1H-stacked bilayer MoS₂ has an interlayer spacing of approximately 0.674 nm, larger than the conventional 3R stacking. This indicates weaker interlayer coupling, which contributes to the direct bandgap. PL measurements revealed that the excitonic emission intensity of the 1H-stacked bilayer is significantly higher than that of monolayer and conventional bilayer MoS₂.

This research suggests that future 2D semiconductor designs can benefit from precise atomic stacking control, offering new strategies for tailoring electronic and optical properties. Such advancements could impact ultrathin light-emitting devices, photodetectors, optical information processing, valleytronics, and quantum functional devices, aligning with the industry's shift towards new materials and technologies in the post-Moore era.

The achievement underscores the capabilities of NCKU's Core Facility Center in advanced materials characterization and interdisciplinary research. The Center provides technical expertise and shared instrumentation, supporting research teams both within and outside the university. Dr. Lin acknowledged the support from the National Science and Technology Council and the Taiwan Consortium of Emergent Crystalline Materials, as well as NCKU's resources and expertise, which facilitated the publication of this research in a leading scientific journal.