Borophene growth on metal surfaces studied by LEEM and micro-LEED.

Borophene is a recently synthesized 2D allotrope of boron. Unlike most other 2D materials, its structure is highly tunable, exhibiting polymorphism that depends strongly on synthesis conditions and substrate choice. This tunability enables tailored properties for applications in next-generation electronics. As the lightest monoelemental 2D material, borophene is also a promising candidate for high-temperature superconductivity. A major requirement for practical use is the ability to synthesize borophene islands on device-compatible scales. One promising approach combines controlled atomic-layer-by-layer growth under ultra-high vacuum with in situ monitoring, allowing observation of borophene growth from nucleation to full monolayer formation. We employed Molecular Beam Epitaxy together with Low-Energy Electron Microscopy and micro-Low-Energy Electron Diffraction to achieve well-controlled synthesis and real-time tracking of borophene morphology and crystal structure evolution. Using this approach, we investigated borophene growth on single-crystalline metallic surfaces, including Cu and Ru.