Synthesis of single-crystal two-dimensional α-Al₂O₃ via a precipitation-oxidation process

The growth of single-crystal α-Al₂O₃ is crucial for a variety of applications in electronics and other fields, while the synthesis of its two-dimensional (2D) form is not easy due to the high activation energy. Here, we demonstrate the growth of single-crystal 2D α-Al₂O₃ by high temperature (high-T) annealing of Ni foils. Tens of micrometers of 2D α-Al₂O₃ flakes grow on the surface of Ni foils, which is attributed to the precipitation of Al atoms from the Ni foil bulk to its surface, followed by the oxidation of Al atoms on the surface. In principle, the Ni foil acts as a solvent, where diluted metal atoms precipitate onto the surface and react with oxygen from the atmosphere to grow single-crystal 2D metal oxides. Our findings may also provide a promising method for synthesizing other single-crystal 2D metal oxides.