Two-dimensional (2D) materials are attractive for photonics due to their unique physical and chemical properties. Vertical heterostructures formed by stacking layers of 2D materials can generate new functionalities beyond those of individual materials and hold promise for next-generation optoelectronic devices. However, the controlled fabrication of vertical heterostructures has remained a significant challenge. Existing preparation methods primarily rely on mechanical exfoliation followed by manual stacking, which suffers from low efficiency, or epitaxial growth techniques that are difficult to precisely control. Organic crystals are designable and have rich interfaces, yet solution self‑assembly favors thermodynamically stable lateral structures over vertical ones. A simple, effective kinetic method for vertical epitaxy remains unavailable.
Now, a research team led by Professor Xue-Dong Wang has proposed a fast-deposition strategy based on micro-space in-air diffusion to address this challenge. The method enables kinetic control of the epitaxial process for preparing 2D twisted vertical heterostructures (TVHs) from perylene (Pe) and 1,4-bis (4-cyanostyryl)benzene (o-MSB) organic crystals.
The key to the strategy lies in temperature regulation. By increasing the diffusion distance between the heating source and the deposition substrate from 150 μm to 600 μm, the deposition temperature on the upper substrate decreases from 120 °C to 110 °C. This creates a high degree of undercooling that substantially reduces the energy barrier for vertical nucleation on the crystal surface, greatly improving the likelihood of vertical epitaxy. The experimental results show that the vertical epitaxy yield increases dramatically to a relatively satisfactory level of over 70%.
Remarkably, the resulting TVHs exhibit a fixed 45° twist angle between the upper epitaxial layer and the lower seed crystal. HRAFM images, SAED, and XRD test results collectively reveal that this specific twist angle originates from the near-coincidence lattice matching between the Pe and o-MSB crystals. The repeat intervals along the [001] and [010] directions of Pe closely match those of o-MSB along the growth directions, minimizing interfacial defects and strain. This unique matching pattern determines the fixed twist angle and provides significant insight for designing novel integrated structures.
The twisted bilayer architecture endows the TVHs with distinctive optical properties. Under 375 nm ultraviolet excitation, the upper o‑MSB (blue) and lower Pe (yellow) layers generate a 490 nm green peak in the overlap region, resulting from optical absorption-reemission and constructive interference between the two layers. Moreover, strong polarization anisotropy and the 45° twist angle between the layers causes the intensities of the 450 nm, 490 nm, and 583 nm emission peaks to vary periodically with the analyzer angle. This enables continuous and reversible tuning of the overall emission color from blue to yellow-green across the CIE chromaticity diagram. These results indicate that TVHs hold considerable promise for future applications in integrated photonics.
This work was supported by the Natural Science Foundation of Jiangsu Province and the National Natural Science Foundation of China, as well as the Collaborative Innovation Center of Suzhou Nano Science & Technology. The findings were published online on August 19, 2026, in Science Bulletin (Impact Factor: 20.7). Doctoral candidate Chao-Fei Xu served as first authors. Professor Xue-Dong Wang served as corresponding authors.
