Confined Crack Propagation in MoS₂ Monolayers by Creating Atomic Vacancies

In two-dimensional crystals, fractures propagate easily, thus restricting their mechanical reliability. This work demonstrates that controlled defect creation constitutes an effective approach to avoid catastrophic failure in MoS₂ monolayers. A systematic study of fracture mechanics in MoS₂ monolayers as a function of the density of atomic vacancies, created by ion irradiation, is reported. Pristine and irradiated materials were studied by atomic force microscopy, high-resolution scanning transmission electron microscopy, and Raman spectroscopy. By inducing ruptures through nanoindentations, we determine the strength and length of the propagated cracks within MoS₂ atom-thick membranes as a function of the density and type of the atomic vacancies. We find that a 0.15% atomic vacancy induces a decrease of 40% in strength with respect to that of pristine samples. In contrast, while tear holes in pristine 2D membranes span several microns, they are restricted to a few nanometers in the presence of atomic and nanometer-sized vacancies, thus increasing the material's fracture toughness.