Two-dimensional (2D) materials are prized in photonics for their unique physical and chemical properties, and stacking layers of them into vertical heterostructures can generate new functionalities beyond what any single material can do on its own. The catch has always been fabrication: existing methods either rely on mechanical exfoliation followed by manual stacking, which is slow and inefficient, or on epitaxial growth techniques that are difficult to control precisely. A research team led by Professor Xue-Dong Wang has now proposed a much faster route.

Organic crystals are highly designable and have rich interfaces, but solution self-assembly tends to favor thermodynamically stable lateral structures over vertical ones — a simple, effective kinetic method for vertical epitaxy has simply not existed. Wang’s team addressed that gap with a fast-deposition strategy based on micro-space in-air diffusion, which 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.

A Question of Temperature

The key to the strategy lies in temperature regulation. By increasing the diffusion distance between the heating source and the deposition substrate from 150 to 600 micrometers, the deposition temperature on the upper substrate drops from 120°C to 110°C. That creates a high degree of undercooling that substantially reduces the energy barrier for vertical nucleation on the crystal surface, greatly improving the odds 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. High-resolution atomic force microscopy images, selected area electron diffraction, and X-ray diffraction 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 crystal growth directions closely match between the two materials, minimizing interfacial defects and strain — a matching pattern that determines the fixed twist angle and offers valuable insight for designing new integrated structures.

Blue to Yellow-Green, on Demand

The twisted bilayer architecture gives the TVHs distinctive optical properties. Under 375-nanometer ultraviolet excitation, the upper o-MSB (blue) and lower Pe (yellow) layers generate a 490-nanometer green peak in the overlap region, produced by optical absorption-reemission and constructive interference between the two layers. Strong polarization anisotropy combined with the 45° twist angle causes the intensities of the 450, 490, and 583-nanometer emission peaks to vary periodically with the analyzer angle, enabling continuous and reversible tuning of the overall emission color from blue to yellow-green across the CIE chromaticity diagram. The results suggest TVHs hold real promise for future applications in integrated photonics.

The findings were published online on August 19, 2026, in Science Bulletin (DOI: 10.1016/j.scib.2026.08.036), with doctoral candidate Chao-Fei Xu as first author and Professor Xue-Dong Wang as corresponding author. The work was supported by the Natural Science Foundation of Jiangsu Province, the National Natural Science Foundation of China, and the Collaborative Innovation Center of Suzhou Nano Science & Technology.