Strain-driven phase transition in porous 2D AST-crystalline sheets: insights from DFTB+ simulations

The emergence of two-dimensional (2D) materials, particularly in the form of nanosheets, has attracted significant attention due to their extraordinary properties that differ markedly from those of their bulk counterparts. Among these materials, zinc oxide (ZnO) stands out for its highly tunable electronic, optical, and mechanical properties. However, understanding strain-induced phase transitions in few-layer systems remains a critical challenge, especially in nanoporous ZnO architectures. In this study, we investigate a novel ZnO-based nanosheet series derived from the porous AST bulk crystal and demonstrate a first-order phase transition between a cage-like (AST) phase series and a flattened (AST-F) phase series under tensile strain. By employing the semi-empirical DFTB+ method, we reveal that this transformation is accompanied by abrupt changes in symmetry, volume, and electronic structure, enabling reversible modulation of both bandgap and pore geometry. Additionally, we evaluate the structural stability, strain energy, and electronic properties of the few-layer nanosheets, offering key design principles for strain-engineered ZnO-based materials. These findings pave the way for the development of adaptive materials with potential applications in flexible electronics, strain-tunable optoelectronics, and molecular encapsulation technologies.