Atomic Layer Dependence of Shear Modulus in a Two-Dimensional Single-Crystal Organic–Inorganic Hybrid Perovskite

Characterizing basic material properties, especially mechanical properties, is the prerequisite for building reliable and durable devices. As a promising semiconductor material, two-dimensional (2D) organic–inorganic hybrid perovskites possess outstanding optical and electrical properties and have attracted significant interest for their wide energy applications. Therefore, a basic mechanical property study of 2D perovskite material will both improve the understanding of atomic layer-dependent property change and guide next-generation novel device designs. Here, we report a direct shear modulus characterization of 2D organic–inorganic hybrid (C₄H₉NH₃)₂PbBr₄ perovskites in the ⟨001⟩ direction by atomic force microscopy. The measured shear modulus of the 2D perovskite increases significantly with the decrease of the atomic layers, especially as the layer number is less than 60. A composite sandwich model to the free surface contractions of the molecular interaction length is built to reveal this abnormal atomic layer-dependent mechanical phenomenon. The characterization method and the sandwich model with a rigid-elastic atomic interaction can be extended to analyze other 2D materials.