Fostering mica exfoliation through biaxial straining strategy with monovalent cation substitution

Abstract

Efficiently exfoliating mica for 2D applications remains a challenge, partly due to a lack of comprehensive design principles based on atomistic modelling of its solid mechanics. In this investigation, we employed a threefold approach: (1) Biaxial straining principles were utilized to compute electron–electron, electron–phonon, and phonon–phonon interactions at crack tips, (2) first-principles calculations were employed to explore the intrinsic relationship between muscovite mica's crystalline structure, electronic properties, ion exchange energy, and exfoliation energy, particularly in the context of various interlayer cations, and (3) experiments were conducted to corroborate the theoretical forecasts. Our findings reveal a compelling correlation between the unit cell size and the ionic radius of the interlayer cation, a phonon-dependent parameter, whereas the bandgap energy, an electron-dominant parameter, remains relatively unaffected. The electron–phonon interactions, characterized by the dihedral angle and size of the hexagonal tetrahedral ring, are influenced by the properties of the interlayer cation, crucially governing ion exchange and exfoliation energy. Significantly, mica featuring H+ interlayer cations demonstrates substantial biaxial strains, aligning with the lowest exfoliation energy, thereby facilitating efficient exfoliation. Our experimental endeavors validate that Li+ intercalation prompts a reduction in number of layers in resulted nanosheets, observed in the order of Li+ nanosheets < Na+ nanosheets < K+ nanosheets. Notably, Li+ intercalation enhances mica's exfoliation into thinner nanosheets. We propose a strategic biaxial straining approach: either replacing the interlayer cation with the smallest cation (H+) or employing larger cations within the boundaries of ion exchange. These outcomes contribute valuable insights into mica's exfoliation mechanisms and furnish a comprehensive guideline for proficiently exfoliating layer-structured materials.