Metal-lattice-heredity synthesis of single-crystalline 2D transition metal oxides

Two-dimensional (2D) transition metal oxides (TMOs) have attracted much interest because of their unusual properties and high-temperature stability. However, due to isotropic bonding in all three dimensions and surface energy constraints, the direct synthesis of 2D TMOs with high crystal quality is challenging. Here, we develop a metal-lattice-heredity (MLH) strategy for synthesizing ultrathin TMO single crystals (e.g., Fe 2 O 3 ) with tunable properties on SiO 2 /Si substrates. The MLH starts with chemical vapor deposition-grown 2D transition metal dichalcogenides (TMDs), followed by unique sequential sulfur-to-oxygen substitution reactions to obtain TMOs, where metal atoms retain their original lattice arrangement and symmetry. Such a process results in growing single-crystalline TMOs coinciding with the morphology and thickness of TMD templates, as supported by in situ optical studies and atomic-resolved imaging. The method can be used to grow many 2D TMOs, including Fe 2 O 3 , V 2 O 5 , Cr 2 O 3 , Co 3 O 4 , and NiO, with band gaps ranging from the near-infrared to the near-UV.