Researchers achieved stable AA-stacking hexagonal boron nitride

Researchers from Pohang University of Science and Technology and the University of Montpellier have made a significant breakthrough in material science. They have successfully created large-scale hexagonal boron nitride (hBN) with a new crystal structure called AA-stacking, which was previously thought to be impossible. This new method uses metal-organic chemical vapor deposition on a gallium nitride substrate. The discovery opens up new possibilities for controlling the stacking of materials, which is important for future technologies in quantum photonics and ultra-violet electronics. The study was led by Professors Jong Kyu Kim, Si-Young Choi, and Guillaume Cassabois. Their research, published in Nature Materials, challenges earlier ideas about stacking in hBN. It shows that specific growth mechanisms and charge incorporation are essential for forming the AA stacking configuration, which is traditionally seen as unstable due to electrostatic repulsion between layers. Typically, hBN has an AA' stacking arrangement. In this arrangement, boron and nitrogen atoms alternate in each layer. The new AA stacked form aligns identical atoms vertically, which was believed to be too unstable to achieve. However, the research team found that using step-edges on the GaN substrate helps stabilize these layers and reduces disorder. Additionally, they discovered that adding carbon during the growth process creates extra charge carriers. This adjustment helps reduce the repulsion between layers, making the AA stacking more feasible. This finding suggests that stacking arrangements can be engineered through the properties of the substrate and the incorporation of specific elements. The new AA-stacked hBN has shown promise in applications like nonlinear optics, as indicated by enhanced second-harmonic generation. It also showed strong band-edge emissions in the deep-ultraviolet spectrum, pointing to its potential use in efficient optoelectronic devices. Researchers believe that this advance in controlling stacking order is crucial for developing high-performance 2D electronic and photonic systems. They emphasize the versatility of the metal-organic chemical vapor deposition technique for creating custom 2D materials with distinctive properties.