Shape Control of Ca₂Nb₃O₁₀ Nanosheets: Paving the Way for Monolithic Integration of Functional Oxides with CMOS

In order to integrate functional oxides with Complementary Metal Oxide Semiconductor (CMOS) materials, templates to ensure their epitaxial growth are needed. Although oxide nanosheets can be used to direct the thin film growth of transition metal oxides in a single out-of-plane orientation, the in-plane orientation of individual nanosheets within a nanosheet-based film is totally random. Here, we show the ability to improve the in-plane orientation of Ca2Nb3O10 nanosheets, and hence of SrRuO3 films grown on them by controlling their external shape. The parent-layered perovskite KCa2Nb3O10 particles were formed in square-like platelets, thanks to the anisotropic growth in molten K2SO4 salt, as opposed to the formation of irregular platelets in a solid-state reaction. The exfoliation of HCa2Nb3O10, which is the protonated form of KCa2Nb3O10, was optimized to retain the square-like shape of Ca2Nb3O10 nanosheets. Electron backscatter diffraction confirmed the improved in-plane orientation among square-like Ca2Nb3O10 nanosheets with the formation of larger SrRuO3 domains. As a result, SrRuO3 films showed the lower resistivity and higher residual resistivity ratio, ρ300K/ρ2K, on square-like Ca2Nb3O10 nanosheets than on irregularly shaped nanosheets of similar lateral nanosheet size.