A wafer scale thin film of ultra-small Sc ₂ O ₃ nanocrystals on a 2D COF with high rigidity

Scandium oxide (Sc₂O₃) has a wide range of applications in metallurgy, chemical industry, electronics and many other high-tech fields. However, most Sc₂O₃ materials exist in the powder or bulk form, while nanostructured Sc₂O₃ has rarely been reported as there is a lack of a common method to control its dimensionality, hindering the understanding of new properties and potential applications of nano-Sc₂O₃ materials. In this paper, we establish a procedure to synthesize a two-dimensional (2D) Sc₂O₃-covalent organic framework (COF) composite film where the crystal size of Sc₂O₃ domains is as small as ∼3 nm. The composite film is prepared by a Schiff base condensation reaction at the sharp n-pentane/water interface using a combination of surfactant-monolayer-assisted interfacial synthesis and laminar assembly polymerization methods. Then the conditions of nucleation and uniform film formation of the 2D Sc₂O₃/COF are explored further. Meanwhile, an atomic force microscopy indentation test shows that the material has a high Young's modulus of 89.1 ± 3.8 GPa, which is much higher than those of the majority of reported 2D polymer materials. We further extended this synthesis method to the preparation of Yb₂O₃ (ytterbium oxide) and/or Er₂O₃ (erbium oxide)-incorporated 2D COF composite films, verifying the universality of this strategy. This work provides an opportunity to vary the dimensionality of many kinds of metal oxides and explore the potential applications of low-dimensional Sc₂O₃ materials.