Size and Chemical Environment Control Nanopore Geometry in 2D MoS ₂ : From Irregular to Triangular Defects

Defects in 2D transition metal dichalcogenides (TMDs), such as molybdenum disulfide (MoS₂), can modulate their optoelectronic and membrane properties. Increased structural complexity and a quasi-2D nature complicate the study of extended defects in MoS₂. To address this knowledge gap, coordination-dependent atomic fingerprints are advanced for undercoordinated atoms in TMDs, enabling the cataloging of nanopore isomers in MoS₂. Combining the introduced fingerprints with extensive density functional theory calculations of etching energies, stochastic kinetic Monte Carlo simulations of defect formation, and chemical graph theory for distinguishing nanopore shapes, predicts the most probable nanopores in MoS₂. A range of size-dependent topologies are revealed from elongated to perfectly triangular, where smaller defects are irregular, while larger ones are more symmetric, exhibiting qualitative agreement with experiments. Moving toward a sulfur-rich chemical environment slows down the growth of larger pores and makes them perfectly triangular, providing an experimental route to control nanopore synthesis. The size-dependent structural order in MoS₂ nanopores elucidated here will enable precise control over the defect shape and size distribution in the material for various application areas, including seawater desalination, gas separations, DNA sequencing, and optoelectronic devices.