"The study shows that cracking in 2D materials is fundamentally different from cracking in 3D ductile and brittle materials. These results cannot be explained with the conventional material failure theory, and we suggest that a new theory is needed," explained Professor Lee Young Hee.
Scientists are investigating which fractures are likely to expand and which are not. At the nano-level, atoms move more freely in ductile materials than in brittle ones. So far, this explanation – the Griffith model – has been applied to cracking phenomena in bulk, but it lacks experimental data at the atomic or nano-scale.
In this study, IBS scientists observed how cracks propagate in 2D MoS2 after a pore was formed either spontaneously or with an electron beam.
The atomic observations were done using real-time transmission electron microscopy. Even though MoS2 is a brittle material, the team saw atom dislocations 3 to 5nm away from the crack tip. This observation cannot be explained with the Griffith model.
In order to create conditions that represent the natural environment, the sample was exposed to UV light. This caused the MoS2 to oxidise. Atom dislocations occurred more rapidly and the stretched region expanded to 5 to 10nm from the crack tip.