Exceptionally large fracture strength and stretchability of 2D ReS 2 and ReSe 2 .

Two-dimensional rhenium disulfide (ReS 2 ) and rhenium diselenide (ReSe 2 ) have gained popularity due to their outstanding optoelectronic properties. However, their mechanical behavior has not been investigated experimentally and many of their mechanical parameters are still unexplored. Here we conducted atomic force microscopy (AFM) indentation experiments and extracted their Young's moduli and found that it is thickness-independent. In addition, we found that both materials are capable of sustaining large pretension. Importantly, fracture tests showed that these materials exhibit exceptionally large fracture strength (32.9 ± 2.4 GPa and 27.7 ± 3.9 GPa for ReS 2 and ReSe 2 , respectively) and stretchability (up to 24.2% for ReS 2 and 23.0% for ReSe 2 ). Therefore, this study shows the superior mechanical properties of ReS 2 and ReSe 2 . Thus, it will open the path for their future integration into advanced applications that will benefit from their outstanding mechanical durability and attractive optoelectronic properties, such as flexible photodetectors, stretchable photonic devices, and strain-engineered electronics.